Which DLCs dor Payday 2? no cosmetic stuff needed!

Well.. there are the two DLC's for music, so I'm guessing that's what you don't want.
The rest adds missions and unlocks more weapons for you to use... if you click on each DLC in the Steam store it will give you a brief description.

if you want weapons pick gage package 1 (weapons including nades) or 2(lmg weapons including knifes), if you want mods pick courier mod, and if you want map it's either big bank (got 1 weapon) or armored transport (got 2 weapon). Correct me if i'm wrong..

All the DLC's are good to have.
You dont have to have the extra mission DLC (armored transport, big bank) as anyone can join a host who has them.

Usually the courier mod pack is recommended as a first dlc, as it adds a ton of new mods to the starter weapons, making a Car-4 rifle a lmg with 60 rounds for example. It'll also make you able to get 3 detection risk with the right mods for the car-4 and a pistol.

If you'd rather go for new guns i'd personally recommend the sniper pack, get the R93 and use a holo sight or something on it. If you're good at headshots you'll tear down shields in no time and come to good use for your team. Just don't use the real sniper scopes, "snipers are for p**sies :3".

That is if you prefer to go loud. If you'd rather go stealth you should get the courier mod pack.

Gage Sniper Pack

Gage Mod Courier

Gage Weapon Packs 1+2

Armored Transport

These are the only ones I could honestly recommend worth buying at the moment. Of them all, Courier Mod is the one I recommend the most as it is the only way to really guarantee getting useful weapon mods you want.

i highly recomend to get the courrier job pack, specialy for starters is an eassy way to get free install mods for your weapons and some of them are really great.