CAP AC
-No firewall/QoS/NAT/DNS/DHCP,i would delegate those task to the RB1100AHx4 dude
-For uses in classroom enviroments,Computer based test
-8x10 square metre room,using both 2,4 and 5 ghz
1.Can the cap ac serve 40~50 active user at once? Just for web browsing,approximate throughput is 2-7 mbps/client

RB1100AHx4 dude
-Use as well,router
-Approx. 30 firewall filter,3 nat,25 mangle,dns server
-100 mbps WAN
-Web proxy cache using the ssd
1.Can the RB1100 handle 400 hotspot user(separated radius server,not using userman),along with equivalent web proxy client & server connection?
Im not expecting exact answer,but if anyone ever face similiar scenario,or even more user can share with me?

Yes to everything. I would go for a RB4011 and have access list rule on the cAPs based on signal strength not weaker than -67. A pair RB750 for CAPsMAN would also be included for redundancy. Play well with frequencies to avoid interference in adjacent classrooms.

RB 4011 in place of rb1100ahx4? Or for "replacing" one of the cap ac?

Well,the reason I'm after rb1100 is because it comes with ssd,which I'm going to use for cache.
(The scenario is when the class taking exam,400+ user would access the same web)
Put unlimited limit on queue from cache,and if the rb1100 can handle that much client connection,then everything is fine I suppose.

I'm going to check the rb 750 for redudant capsman.