I haven't had a chance to load up a Mikrotik AP with 50 clients yet...so can't really comment on this much, but seems like it should be fine and I think others have come close to this..comments anyone? This would get you there if your clients are evenly spread around your tower (to balance between the 4 APs). You might want to consider finding an additional tower location for future use in the event that the majority of your cutomers end up only being able to connect to one of your APs - unless this isn't likely to happen in your location. Still, if you are considering a lot of bandwidth, it might be a good idea to look into it anyway.
I think it would be good to hear from some others who have had some experience with a lot of clients on a sinlge Mikrotik AP. Anyone?
Thinking after I get everything worked out and anyone else have any practical examples, it woud be good to summarize all the infor into the wiki as configuration examples of capabilities.
This would be nice to have...as well as what works, what doesn't, and some practical limitations (for ptmp) people have run into.