Liquid cooling suggestions/tips?

If you're not overclocking your CPU, I would just stick with some non-conductive thermal paste and the Hyper 212 heatsink. Though I suppose if you have the lust to build exotic things then it can't be helped. To me, 'exotic' is a micro-ATX case, haha.

"I am especially interested in the input tubes. Sadly this is the first I have heard of those... and I really have been running searches like a madman on the subject. I probably should have just opted to find a reliable book or the like. I picked up a two-pump reservoir combo, but it will reside in the 5.25” bay… and refilling there would likely prove a greater pain than I would prefer to manage."

My experience has always been with stand-alone reservoirs and pumps. My current setup has two large cylindrical reservoirs, similar to EK's Multioption X2 if they aren't already that specific model. Because of the multiple flow-path options I opted to connect an extra tube from each routed to the back panel, because direct access to those reservoirs was unfeasible. Then I learned first-hand how air-pressure works. I have to take small-nose pliers to open a cap on each reservoir in order to fill them in a timely manner.

If you're wondering why I have two reservoirs, it's because I have two completely separate loops running on my rig (one for video cards and motherboard chipset/voltage regulators, another for CPU and RAM). Yes it's monumental, and yes it's monumentally stupid. The Corsair 800D I pack these in is a massive case, and even it could only barely handle everything I put in it. Sure on a rainy day with the window open this thing will never rise above body temperature even under load, but it weighs a ton and is a pain in the ass to move and dismantle. A lot of what I said earlier is based on my experiences with this setup.

"My final chassis choice was the Corsair Carbide 780T. It provides excellent ventilation, and I can house either a 360mm or 280mm radiator topside or front. I have opted for the top mount, and my air cooling fans will remain in front. "

This will probably work well for you. If you hadn't already got it I'd have advised a larger case such as the 900D, just to have more space to work with. Then again I've never used drive bay reservoir/pumps. Smaller cases are also easier to ventilate and drain. I'm a little concerned that there are only two drive bays available. One for watercooling, another for what I presume will be an optical drive. No fan controller. I myself wouldn't be able to live without my Zalman ZM MFC3. Then again, fan controllers are typically just more wires to tangle with and inevitably fuck up at least twice.

Top-mounting the reservoir is usually the best option in most cases. If you want to go really bonkers, do what I did and cut holes for another intake fan in the side-panel plexiglass. It's delicate work but having cool air flowing directly onto the motherboard is reassuring.

"The air cooling is sufficient, but I have not run any full load testing to see how the temps fare under stress. Thus far the hottest temp I have recorded is 73° C on my second GPU. It's not high; but I think there are two things worth noting here. The first is as I mentioned in my reply to StarshipGhost's advice above, my primary focus here is on the experience in the build. Admittedly, my current components are not likely to require the water loop unless I do some heavy OC-ing. The Haswell-E is rated at low average temps, and the GTX 980’s are running on 30% less juice and are inherently (and significantly) cooler than their competitors and predecessors. Just the same, that 73° was hit while my son was tackling Garden Warfare… not exactly a title I would call a card killer. The primary card was still under 50° C, but perhaps the second card will benefit for the liquid cooling under higher strains."

Haswell-E. 980's in SLI. Not exactly a potato is it. Having water cooled for so long (since '04) I can't recall ever having a component at 73 degrees. That sounds functional but not healthy. Another benefit of watercooling that many people miss is that lower temperatures help components last longer without failure. Usually. Theoretically.

Also, look into upgrading to a G-sync capable monitor at some point in the future. Haven't had the chance to experience it for myself but all reports say it's The Future™.

"Now, back to points two and three, everything (with the exception of the RAM spreaders) is EK and my tubing and fittings are all in sync."
That's what I would have recommended. EK are awesome.

"In regards to the RAM, I will not be overclocking. In fact, with the DDR4 performance (IMO) is likely to be sufficient for a while with high demand games. Again, the decision here really rested on my desire for the experience more than anything… but I did consider a return to some direct cooling fans… I just figured, “I’m all in” at this point, hence the RAM blocks."

RAM these days is usually never the bottleneck, even at standard speeds. And then only for games that are not graphically challenging. With a Haswell-E and two 980s, the 10fps in Skyrim you'd gain from fast RAM won't be noticeable since you're already pushing over 100 anyway.

DDR4 is a bit of a mixed bag at the moment, much like how DDR3 was when that first came out. Sure it's fast, but the currently available latency timings are trash in comparison so there's little noticeable performance gain over DDR3. That will be fixed down the line though. DDR4 does run at lower voltages though, i.e. cooler. So that's great. You'll also likely not have to replace your motherboard when you build your next rig a few years down the line and DDR4 becomes mainstream.

"Another insight you have given to me of great value is the tubing suggestion between the cards. Again, this is one of those lessons I would otherwise likely have learned the hard way."

I learned it the hard way so you wouldn't have to. One of my video cards started blue-screening when SLI was enabled. It was a two-man job to pry the whole contraption out, with each of us prodding the pci-e locks with screwdrivers. And since EVGA's replacement card wasn't the same model (and had an extended PCB that my EK block wasn't compatible with) I had to cobble together extra tubing to go to the one remaining card.

But I think I may have exaggerated the scale of the problems associated with triple-blocks. When the card failed, it's a massive inconvenience. But only an inconvenience. I had an over-sized case, stuffed with an insanely overcomplicated system, having suffered hardware failure that may have been my idiotic tampering, and inconvenience from EVGA due to the PCB dimensions. None of these conditions apply to you. As a means of cutting tube clutter and improving aesthetics it was marvelous when everything was working, so that experience won't stop me from re-using it in my next rig. I wouldn't recommend a triple-block for beginners, but only because I recommend starting with loops being as compartmentalizable as possible. You already have the block, so just use it. At least you know what to do if something does happen.

"still, your point makes me consider the value in being able to easily cut off that flow."

It sure beats having to drain the entire loop whenever something needs changing. But again, get tube clamps, not valves. And while a shorter loop is better, always give some generous slack.

"I will also make a point to pick up some extra parts. I had considered that… but with costs rising quickly… I was justifying my failure to pick those up at the start… you’re definitely right though, and I am certain the regret later would be worth avoiding."

Spare parts are like guns and condoms. It's better to have and not need them than to need and not have them.

Oh, and a few more things.

• If you have trouble slipping the tubing onto the radiator ports, trying putting the tubing under very hot running water to soften and expand it. This won't save your fingers from getting sore but it will save time.
• Never, ever, ever used colored tubing. Likely not an issue in your case, but for anyone else reading, when algae starts growing in your loop you'll want to know about it.
• On the subject of algae, don't flush chemical cleaners (alcohol, vinegar, whatev) through the line. Those will corrode your blocks. You'll need to drain, dismantle, and manually clean your system if it's in the tubes.
• Put rubber between the pump/reservoir and whatever it's resting on/against. It's going to vibrate and if it's not properly set you'll have to suffer annoying noises. There's no general solution. giant pads, tiny feet, you'll need to experiment.