>> FWIW, what I want most in Solvespace is a way to do chamfers and fillets.

I've outlined a function for that and started to write the code. At a high level it's straight forward, but the details are complex. It'll probably be a year before it's done.

>> And a way to define parameters (not sure if that's already possible).

This is an active work in progress. A demo was made years ago, but it's buggy and incomplete. We've been working out the details on how to make it work. I hope to get the units issue dealt with this week. Then the relation constraints can be re-integrated on top - that's the feature where you can type arbitrary equations on the sketch using named parameters (variables). I'd like that to be done this year if not this summer.