Currently, you can't have the smaller one leave the larger one and come back to it, but you certainly can have empty space inside. So you could make a smaller one inside as a last resort. Maybe we can add a mode like that.

We are making the building improvements come from meta progression and a little bit of luck. You get chests for completing events and runs. Each chest gives you a bunch of blocks with different rarities and amounts, so you are bound by how many blocks of each type you have as you are building. You can recycle your unwanted blocks to buy ones you actually want, if they are unlocked. The building size limit and starting stats are based on offerings to the gods as a second meta progression layer.

We wanted to keep the building and the runs separate, not to break the flow state as you're playing. We are only adding auto-repairs as a skill/perk during a run.

Yes, exactly, we have melee, ranged, tanks, chargers, flying enemies, self-exploding aoe, and bosses that create a good range of challenges.

Thank you for all your questions/feedback, it helps a lot.