Some very good points. I recall that the mainnet once had a gas per block limit of 4.7 mil before it was increased. The increase is something that is voted on by the miners, and has been fluid over the years. (Btw, it is something very similar to a block size limit in BTC, although it limits the storage + CPU usage, rather than just storage like in BTC)
About the point on using floats, one should never use floats when working with money, this is because floats are not precise and result in rounding errors (eg. 0.1 + 0.2 results 0.30000000000000004, see for details http://0.30000000000000004.com ). One of the simplest approaches to solve it is to work with the smallest units, so if working with dollars then you can use cents and that means you can use integers which give more precision, which is how Solidity currently deals with it, by working with the smallest unit of Ether which is 'wei'. Some of the units listed here https://etherconverter.online