grayfoxx, teams will have 20 players already. Up to 360 players will already be released into the draft pool when keepers lists are presented, and teams drop from 35 to 20 players as they await the draft. While some of those cut will be retiring, and some scrubs, many, probably most will be useful players.
We then add 250 additional players, some of whom will have low PA or IP because it is their first season but will then go on to have solid or great careers. Others will have full-time or nearly full-time PA and IP from the first. Teams will likely have kept mostly full-time PA and IP players except for a few future stars that they are waiting to have mature into full-time players. So most teams really will only need an additional 5 players to get to a workable team and instead will find a draft pool of 15 players for each team to draft and well over that number between the newly added names and the ones that were released from rosters, plus many who were not drafted initially, and who have continued to move forward in time, some numbers of whom are useful.
So I think 250 should be enough of an addition each season. Obviously, if we find that not to be the case we can vote to change it and increase the number of new draftees in future drafts.