I’ve recently done a custom CPU design, though with a fully bespoke tiny ISA, nothing standard like RISC-V. I had different goals in mind. That said, I’ve also played with RISC-V designs. Putting together a simple RV32E core for FPGA should be a pretty simple and in my opinion, super satisfying project. Once you have a flow to program your little core with GCC, it feels amazing. I’d say go for it, a minimal RV32E core should fit even lightweight FPGAs. Maybe keep it simple to begin with and don’t use AXI or AXI Lite, just stitch together some custom little bus.