Hello........ just an FYI about running NL ring games that I have about once a month, I cap the buyin for a $.25/$.50 blinds game at $40 this seems to be about right for everyone that plays....... some will buy in for much less as low $5 at times but usually most are between $20 and $40.
I have not set a max number of rebuys though........ everyone is comfortable at this level and everyone usually has about $100 to $200 with them for the evening. This amount varies by player and what they are comfortable with. The rebuy limit is still $40 even if most people at the table have much larger stacks, another game I have been to will let you rebuy upto the median (not the average) $ chip stack in play.
We usually have a $20 NLHE tourney first that usually lasts around 4-5 hours for 24 players and for those who get busted early I have another table to start ring game on because they dont really want to leave that soon

This ring game usually lasts several hours (3 to 6) after the tourney so I must be doing something right
Regarding chip quantity tho......... my personal experience is that you should have at most 3 colors in play for a ring game, usually only the $.25 and $1 chips for my games are needed, having enough $1 chips is key. In other games I have been too the higher ($5) colored chips tend to be hoarded by players not wanting to lose them.

So by having only 2 colors in play this is not a problem and most people arent hoarding them
For computation sake take the number of starting chips/player you plan to use and multiply the number of players you will have, then I recomend at least 2x that to cover rebuys, this seems to work well for me. However you could make a case for not needing that many low ($.25) chips and just make table change too
