That's really cool. I never tried kitbashing and painting (too messy for me) but I did dabble in building mecha out of Lego back in the day. Getting them fully articulated and proportional was a challenge, and I especially loved trying different methods of making hands.

The coolest one I ever built was about 15cm tall, fully poseable, and fit a minifig pilot.

I still have all that lego, but nowhere to set it up, so I haven't built anything in years. :(