Definitely get Stacks. It’s a complete no-brainer. There’s probably no other must-have plugins at this point for you. But there may be several “stacklets” that you want to use. Stacks comes with a generic collection of stacklets, but there’s many more out there. One place to get ideas is here: https://stacks4stacks.com. Some are free, some paid.
However, there are many other fine Stack developers that you may want to visit at some point include Joe Workman and several others.