Steam just has all FO:NV DLC on sale and I want to get the main four, but I'm unsure about Courier's Stash and Gun Runner's Arsenal.

What are your thoughts on them? Do many mods rely on them? How popular are the mods that do? Specifically, does the JE Sawyer mod need them or does it only need the main four?

The J E Sawyer mod requires all DLC including these two. It moves the Courier's Stash items to 4 different locations around the Mojave so you don't get their benefit early on. And the GRA weapons are always interesting.

I guess that settles it then. Thank you for the answer.

They are both awesome dlc's, great weapons, new achievements and decent few items to start the game with, or just some cash if you want to sell em all off.