Network Proposal help

I am trying to come up with a better design for the network. there is two wireless routers as of now i want them gone. There will be two airport express stations connected to a stereo system each. an airport express for the offices and a time capsule for mac users to backup their systems. we right now have the network open for everyone. the time capsule does have the option for a guest network which looked nice but i would want two networks over all airport stations, so staff will have their network with what they need and guest will have an open network to just get online, is this possible? staff computer will be moved around a lot and i don't want any limits on them

also, on the airport express with airtunes we would want to make sure only curtain Macs will only play music through airtunes, is this possible.

i would also like to know if there is some way to set everything up there and when i am told that there is a problem i can be at home with my macbook and connect to remotely change settings in all the airport stations?

i did read apple's site for time capsule and it was making it sound like there is a limit of 50 users, is this true or am i misunderstood? if so is their a way to increase this because we do need as many as we can get, 50 will not cut it. we have about 40 or so that staff needs in a day and when more then ten guest connect we do not want problem with the few staff that don't come till later.

I am including a quick diagram to give a basic idea. please don't give guesses i want to be sure that it will not be a problem, i don't want to look bad. if you need a better understanding let me know and i will explain much better. thanks!

Diagram