FO: New Vegas, mods corrupted my save games before. Any advices for a new start?

May I give you an advice? Play the game without mods :D

game is made to be played without mods .... if you wanna troll into the game get mods then

use the Nexus mod manager, it will help alot keeping your mods in order, also make sure to use the 4GB launcher if your are using a lot of mods... and have more that 4GB of memory xD, fixed a lot of crashing for me.

PS: i play mostly with graphics mods, 2k texures, better faces, better sound, better colors.. etc

That's just the way it is with mods, some will break your saves or the game itself and that hasn't changed. The only "safe" mods are for cosmetic changes or mods that add completely new worldspace and items without messing with what's already in the game, anything else and you run the risk of glitches.

Best thing to do is read the comments for a mod before you install it and see what issues people have run across while using it then decide if you could deal with those issues if they happen to you.

It's just the way that the game handles content: if you have a save that contains references to content that no longer exists, say pointers to item addresses that no longer exist, it creates an exception that the game is not configured to handle. It's not as bad in Skyrim, which was configured to handle these sorts of things better, probably for ease of use with the Steam Workshop, but you can still have issues such as inventory weight not matching what you're actually carrying. It only gets worse the more intricate the modification you are using gets. That is why in general you are advised not to uninstall mods and then load a save that relies on them, and to always make a save before you install a new modification, and then continue off of a new save slot.

Also, in my experience, I'm not sure what mods you have actually ties into the 'back-up' you make. If I had to guess, when Steam installs a game, a record is kept of what files are installed by default [maybe the checksums as well] and it uses this log when creating the back-up. That is usually why, when uninstalling a game, data not created by the install, such as modifications, alternative launchers, and configuration files are left behind.

If you use "public-approved" mods, they are usually safe. Always check the mod's description for conflicts, how to uninstall it and what problems (if any) could arise in doing that. Install only mods which you plan to use, since most of the time removal can give errors (which may or may not break your saves, but try to minimize the risk). Absolutely read a guide on how to mod. Lots of issues come not from the mods, but from lack of knowledge on how to mod.

You mean the same Fallout that I have two versions of in my library?
One for regular and for Ultimate?...

I would recommend you watch Gophers "Fallout NV: Tutorials for mod users" Playlist:
https://www.youtube.com/user/GophersVids/playlists or
https://www.youtube.com/watch?v=I-3c1a9cLL8&list=PL0E5E8CA384409B11

I heard there is some sort of problem that can corrupts saves on New Vegas after the amount of save files get too far or something similar to that. I have no idea if its true, but I use one mod called CASM:NV which is a save manager that creates multiple auto saves and keeps saves <1000 I think, to stop any likelyness of corruption and keep a save file to fall back on.

Also I use the Yukichigai's Unofficial Patch which probably helps stuff.

I also usually keep at least 6 saves going at once, so I have multiple different ones to fall back on as well. I would also make sure your mod list is correctly ordered.

Good luck