Hello!
>> Can I create a guest network and create bandwidth limits per SSID and per user using Aruba Instant mode?
Yes you can! Guest user with either PSK, or Captive portal - authenticated user login or just acknowledge terms.
BW contracts are split in upstream/downstream and defined total for the SSID, for the radio or for the role. If added to the Role it would usually mean shared among all users on the SSID.
>> I need any aditional licenses or software additional to the APs to acomplish this requirements?
Nope! Just plug and play! :D
>> Which Aruba AP could you recommend me?
That depends alot.. 50 users in an open environment/cubicles just doing normal office applications? Or 50 designers working on and sharing 15-50 Gig files?
At this time tho I would say either 300, 310 or 320 series even if you don't need Wave 2 now it still gives your solution a longer lifespan.
Follow this link for details and a product finder.
http://www.arubanetworks.com/products/networking/access-points/