The more people join, the lower the rate of return[1]. The max inflation is about 1.71% annually, if 100M ETH stakes. Total supply right now is only 115M.

Net issuance will be lower than that because some transaction fees will get burned. It's possible that the supply will actually decrease.

There's no limit to the amount of stake other than the ETH supply, but they're talking about setting a limit of 32M ETH, just because it'd be more efficient and they don't really expect it to get that high anyway. Under that plan the validators get automatically rotated if >32M stakes.

[1] https://docs.ethhub.io/ethereum-roadmap/ethereum-2.0/eth-2.0...