I’m going to apologize in advance for the long response, but hey, this is what the forum is for, right?
These are all great modules (I own almost all of them!) that you should get plenty of use out of. The thing with modular is, everyone tells you to start with one or two modules and fully learn them, only adding more when you’re absolutely sure what you want. There’s some wisdom to that, but I took the opposite approach: going nuts with it and getting a lot of stuff that looked cool and useful, then diving in and seeing what I could make. It’s worked for me and is still a ton of fun years later. Don’t overthink it or second-guess yourself too much. You’ve already selected quality parts, and you’ll definitely be able to do cool stuff with it.
I just have a few suggestions. First, I would strongly consider getting a stereo mixer module, especially because the Pittsburgh Modular Outs module has stereo inputs. I have the Doepfer A-138s mini stereo mixer, and it’s solid: four channels with level and panning controls in not much space, and you can go straight from that to the Outs module.
Second, the only questionable inclusion with the others is Grids. It’s a great module for triggering drums/percussion, but I don’t see any dedicated drum/percussion modules. Of course, you can use Peaks to get one or two drums and some other percussive sounds out of Elements, Plaits, and Rings, but that will either remove one or two envelope generators (Peaks) or melodic voices (the others). If you want some dedicated drum/percussion modules, 2hp have a line of reportedly great and reasonably affordable modules that won’t take up much space. An even more space-efficient and cost-effective solution is the soundmachines SD1 simpledrum, which packs in six channels (each with multiple sound options) in only 6hp and is easy to use. Frankly, the sounds themselves are not universally great, but there’s a lot of variety, and it definitely gets the job done. There’s also onboard reverb (definitely not the best when extremely wet, but adding a little is fine) and a bonus synth mode, and everything is mixed to a single output. It was the first rhythm module I got, and I still use it more than any other because it’s easy.
Have fun! Modular is a blast.