why not have it so that you must mine for an account
by this i mean, the number of accounts available could be determined by the number of coins in circulation thus you dont bankrupt the system though this doesnt address account spamming.
But seriously onto what I have to say
You should separate the population into 2 categories, citizens and denizens; one exists and the other contributes.
You must then separate citizens into 2 categories, populus pluribus and oligarchs; those who have and those who want.
Denizens should be subject to standard tax policies in addition to a prefunded estate tax (cause they will die at some point and we don't know when that is other than account activity) and do not receive subsidies for being below the predefined coin amount. Furthermore why not institute a basic bank policy, balances below value x are penalized. So lets say that we instead penalize accounts below the threshold to avoid wasting coins on essentially useless leeches.
However I suggest that the value be any account below 10 coins.
The issue for me currently is I don't know how many coins are going to be generated so I have to guess really with the numbers but yeah.
Furthermore what should define citizenship should be account activity.
Account activity should be key to citizenship IE you aren't part of the community unless you sent or received coins over the past x cycles.
Citizens should be subject to all previously stated policies as you mention in the OP. However I suggest that the base account should be 100 coins and thus anyone with more than 10 coins and less than 100 will start to gradually move towards 100. This gradual increase itself will not be taxed.
Oligarchs are those who at any point control more than 25% of the coins in circulation will also be subject to demurring on their sends and receives to help the system function and not run out of cash.
^and here is where I ran out of steam.
To be honest after writing this I really feel like the whole exercise is sorta tired. I am just gonna stick with mining bitcoins until this actually comes out and then we may see.