Okay, first off: I have never used a mod in my entire life, but after discovering that my laptop can run New Vegas on full settings, I really want to download some. Now, my problems are these:

1) How do I properly install a mod?
2) Can I install mods despite that I must run Steam in order to launch and play New Vegas?
3) Since New Vegas goes through Steam, will using mods mess up Steam (or just potentially New Vegas game files is not installed properly)?
4) Aside potential bugs or glitches that can occur, should I rather just not use mods (since I an idiot regarding this)?
5) Does it depend upon what kind of mods I use (I know some require other mods to be installed or the DLCs)?

I looks like you haven't actually tried to use any yet, so... just try? Ask questions after you try if you run into problems, not before- and you're unlikely to run into problems if you read readme files and pay attention.

1. I suggest watching http://www.newvegasnexus.com/downloads/file.php?id=42832 of videos to familiarize yourself with how to install mods for NV.
2. Yes
3. No
4. Life is too short to not mod your game
5. ?