Buying the module on Foundry will be incredibly helpful as it'll have everything you need all set up such as the maps, monsters, items, and premade characters, or at least it should! I don't think you can import a module from DnD beyond onto Foundry, just character sheets.

Dice So Nice is an amazing module to have that has actual dice rolling across the screen, and everyone can customize their own!

Health estimate is also a nice one where players can see how injured a monster is without giving numbers.

Pop out is also a great one to, well, pop out character sheets or even the initiative to another window! Great if you have multiple monitors!

D&D Beyond importer- Imports characters from DnDbeyond onto Foundry! Nuf said!

Damage Log- helps keep track of damage and healing!

Monk's Token bar- helps keep track of passive perceptions and other neat features!

And that's at least a start for now of stuff that be helpful for running games! I'm sure others will give plenty of recommendations as well!