There's no minimum, in fact we're going out of our way to make it easy for casual games to get in on this fair launch. We're actually implementing a cap right now to make sure that we don't let whales come in and overrun everyone else's voice or attempt a hostile takeover.
Realistically speaking, Ethereum mainnet gas fees makes things a bit difficult for smaller gamers to participate in, which is why we're subsidizing new members as part of our Phase 0 launch proposal.
Star Atlas will live on the Solana network, why are we using xDAI and mainnet tools?
The Solana governance module is still undergoing review at has not yet been merged into the main Solana repo. (It's still in development.) The UI has also not been published yet, so it's a huge risk to trust funds to it until it has been battle-tested in the wild.
Once there is working infrastructure that will allow us to coordinate activities on Solana, any member can create and sponsor a proposal to migrate the dao there.
What about DAO taxes?
We would refer you to this article from TokenTax. The answer is that DAOs are currently untaxed entities, (this may change!) but individual members should consider any direct payments such as NFTs, governance tokens, or other payments as taxable events.