If I remember correctly there were 24 team in MLB in 1970, which means that 24 teams in this league will likely lead to difficulties in getting enough PA and IP for everyone. Wouldn't starting with 20 be a better idea, or even 16 and then expanding when MLB next expanded ?
I am in either way, but people may be thinking about playoff spots - not as relevant an issue in progressives where the goal is only nominally to win the pennant every season, since everyone goes through bad patches of seasons and rebuilding phases - instead of the often crucial question in progressives of making sure there are enough available players.
Otherwise, as in many leagues that begin with 16 teams in seasons when MLB also had only that many, your suggested maximum keeper roster of 22 may not need to be enforced. We could be lucky if we have 22 players for each team. If the DH will also go into effect in 1973 in the AL, that will put yet more pressure on available PAs and available players.
I at least, and being a late arrival here, would not want to exclude anyone that is already in (including myself !) but if we are only at 16 I would say, fine, we can decide to expand even in 1971 if we really want to, or else if we are just under 20 guaranteed owners in, let's get to that number so drafting from 24 MLB team rosters we all know we will have adequate players.