Really depends on what you want to do. People have big aspirations to grow in rooms and harvest pounds at a time, but it’s usually not as easy as it looks. In my opinion you’d be better off moving to small space and trying to do it well if going indoors. Once you get your feet wet then see what you’d like to change before going big.
It’s seems to be that people struggle moving inside from outside or outside from inside. Not really sure why, as I’ve only grown indoors. But you can and probably will spend a small fortune getting an indoor grow setup properly. I would just say to do research, and spend your money wisely. It’s likely that any shortcuts you take will eventually lead to you replacing. A pound per 4x4 is reasonable harvest expectation for someone with a little experience and decent equipment. Depending on plant count and veg time you can plan to harvest a single space 2-4 times a year. If you grow perpetually with multiple spaces like 6 times a year with short flowering strains.
That being said, I would start with something like 3x3 and about 300 watts of good led lighting. Grab something like a 6” ac infinity fan and a decent carbon filter. From there, depends on whether you wanna go soil, soilless, or hydro.