Welcome @benjaminjamesgreen. I would first recommend planning long-term, i.e. not what your current budget is, but what you want to achieve. Anyone who is into modular quickly finds out that money and space quickly disappears. With that said, most will tell you to invest in a larger case from the get-go. You WILL want the space eventually, and you can fill it with blind panels in the meantime. The TipTop Mantis is almost always the recommended starter case around here. 2x104hp, inexpensive, and great power supply with a decent amount of power headers.
A second recommendation would be to get a dedicated drum machine instead of trying to include drums in your modular right off the bat. The drum modules you have chosen don't have a lot of patch points, and so their sound design capabilities are very limited. They're also very tiny. That's not very fun. Get a more versatile drum machine that you can clock and interface with your modular for now. You can always invest in better drum modules in the future. Most beginners try to pack too much functionality into a small space (I did it too). For something small like this, focus on developing an excellent synth voice and try to make it as tweakable and patchable as possible. Plaits is always a good starting point. Also, you probably won't need an output module if you get a good quad cascading VCA to double as a mixer.
I've put together what I consider to be a good STARTING point for a modular synth. It overshoots your budget, but I promise that is going to happen anyway. And, you don't need to get everything at once. When you start patching, you will discover what you need to buy next. Some of the others in this forum will probably have recommendations and suggestions for budget friendly alternatives too.
Have fun and good luck!
Edit*
This build assumes that you will be using the Disting or uO_C Piqued for the envelope functions. I have added a Quadrax envelope generator but it's not showing up above.