I am currently using the Nexus Mod Manager to download and install all of my Skyrim mods. I downloaded the 4GB LAA mod using NMM. Do I still need to use the 4 GB.exe to launch Skyrim, or does the NMM somehow automatically use this when I launch from Steam?

This is not a dumb question. I don't know the answer, but you might want to post the question over at Nexus, if you haven't already. The people over there know more about their manager.

You use 4GB Skyrim to launch Skyrim. NMM is just a download manager nothing more.

That is not accurate. You can also launch the game through NMM. So far the options are the main launcher, SKSE and custom. I haven't messed with the custom option.

They do have plans to add the ability to package mods through NMM as well, but this is still very much in BETA.

4GB launcher can't be downloaded with NMM because it's not a typical mod. NMM should only be used for mods that say "Copy and paste to Data folder" in their installation instructions.

Mods that shouldn't be DL'd with NMM:

• Script Dragon Plugins
  
• SKSE Plugins
  
• ENB Series/DLL Injectors

I agree with most, but the 4G extension can be download by the manager because it doesn't require a target directory to work. Although you don't need to use it, it is working way to get it.

Plus every now and then there are mods that come with different options, such as Vurts Flora Mod ex different styles of trees. So these shouldnt be DLed with NMM either

You picked the exact wrong example.
That mod actually has a version with scripts that let NMM users pick their options using a menu system during installation.

Otherwise you'd be right. Mods that have various installation options, unless specified in the description should probably be downloaded manually.

Depends on the directory structure they use PISE can be installed using NMM and the options are in there own directory within DATA to be moved around. Still saves a few steps.

Thanks for the info, everybody!