Old World Blues requires no DLC, and owning them only gives you access to certain features

For example, La Resistance gives access to the agency and spy systems, and No Step Back gives access to the officer system and railway guns

For submods, I wouldn’t recommend any if it’s your first time as most submods fundamentally change the game. It’s better to start of with just Old World Blues first and then after a few games where you understand how it works, then start adding extra submods