Some questions about making givaways.

First: https://www.steamgifts.com/bundle-games
Second: you get an option to store a gift in your inventory when you purchase a game. You send it after the winner is chosen.
Third: not really, too many to list.
Fourth: level drops due to changed value shouldn't be much of a problem to you if you don't intend to give away only the newest games. Vast majority of the ones that have been around for a while should stay the same value, with few exceptions.

First: There is a bundle games list that people have already mentioned - but keep in mind that games can be added it to it retroactively. If something seems like a really amazing deal then expect it to get added to the bundled games list at some point.
Second, third: Already answered very well.
Finally: People can sometimes lose CV if games are added to the bundled list, reduced in base price, etc - but it won't make a lot of difference for most people unless you are actively trying to exploit glitches, etc.

I'd like to add to number 2: due to new stream restrictions, not all games can be added to your inventory for gifting later. (If I'm not mistaken, all the VAC protected games can be gifted only directly, if at all). The option to add to inventory also won't appear in case of steam "bundles", in which you get a discount for games you already own. To give an example Civilization V complete is such a bundle (it can still be gifted if you buy key from a retailer though).
A small add to number 1: games usually get added to the bundle list if they are either in a bundle (high tier might be an exception though) or they cost 5% or less of the regular US price in any store from any region (for example, if a game is 90% off in the steam store, likely, the price for a copy in Russia will cost less than 5% of the US price without discount and thus will be added to the bundle list. Check https://steamdb.info/ for regional price info if you see something with very high discount).