Is it safe to use NMM for mods that I find on this site or should I stick to installing manually? Thanks in advance.

NMM has no "download" function for the gun network.

I install everything manually. And then use FOMM to fix the load order if anything doesn't fit.

i always use nmm with all of my mods its best

for the gun network you cant use mod managers because you install manually but you can manage the plugins with nmm easily without problems.

Try using mod organizer, you won't regret it, there is no safe or wrong way, if you install something wrong you can always uninstall without losing other mod file, because he doesn't touch your game folder.

I always use NMM,
I put the mod in my mods fallout mods folder where all my mods are stored and then activate them via NMM, they will always been shown in unassigned if you don't use the NMM downloader

Yes you can use NMM but just make sure the files in the archive are in the correct order before adding it to NMM.
Keep in mind that NMM and even FMM like to simply extract the archive for you so if things are not correct in the mods archive then they will also install wrong, Sept they keep track of what belongs to what mod for easy uninstall.

I would very highly suggest Mod Manager tho cause it allows for a far greater amount of control to the point you can prioritize textures and bsa's for a more custom experience plus it does not install anything to the actual game installation, Instead it uses a virtual file system so Fallout can see the mods without them ever touching the base game.

Oh and if the archive is not organized correctly then Mod Manager will tell you and let you move stuff around to fix it.

EDIT: Right! it also lets you make "mod" profiles with the option of them having saves kept separate from any other so you can have many different mod configurations at the same time! Just change the profile!

I'm an avid user of Mod Organizer, it's an amazing mod manager. Would always recommend, has a short learning curve but once you got it down, you'll never go back to anything else.

I do personally prefer the use of NMM, for putting 'em up together correctly, and in case of any problems I give a run with BOSS.
But sometimes manualy checking mod by mod and organizing them by yourself is better for you and your game is much less likely to suffer with it. (: