Sims 3 64 bits freezes and flashes

@Dangbe28  I would suggest being cautious with both mods and custom content, but there's no reason you can't use them at all.  Lighting mods are probably not a good idea, but any mod from NRaas is fine, as are most mods from Mod the Sims that say they're updated for patch 1.67.  You should absolutely test them out in a new save (other than NRaas mods) to be sure; I'm just saying you're unlikely to see any issues.

The same is true for .package-based custom content: test it in a new save to make sure it's okay, and actually use it on sims rather than just having it in your game.  If it's fine, keep it.  Even if you miss an issue, a .package file is simple to remove.

For .Sims3Packs, as in, what you install through the launcher, I'd strongly suggest testing everything in a clean user folder before letting it anywhere near your saves.  The problem here is that when you get bad cc this way, it's difficult to remove, so the best approach is prevention.  Move the entire Sims 3 folder out of Documents > Electronic Arts and onto your desktop, open the launcher to spawn a clean folder, install what you want to test, and before doing anything else, see whether any extra items installed alongside the ones you wanted.  Bad cc can attach itself to other cc or to households or lots.

If you're satisfied you didn't get any stowaways, load a new save and check out the items.  Make sure sims are wearing them, or objects are placed on the active lot, and play for a little while, maybe a sim-day or so.  You can test a handful of items at once, to make this less tedious, as long as you remember to try them all.

If everything looks fine, you can then delete the new Sims 3 folder, restore the old one to Documents > Electronic Arts, and install the new content into this folder.