1 Depends on hardware? (as far as I know. no limitations)-
2. like in all software, yes, but no big hassle, that you will notice in everyday use. Biggest issue, and pain,. is MT support for SNPMP
3. Try it your self. Its powerful, if you setup a lot manualy. ITs also usable without setup annyting (other than ip,user and pass).
http://wiki.mikrotik.com/wiki/Manual:The_Dude