QoS - beginner question

hello,
I know how to setup my Astaro, I've experience with firewalls and the content filter, but with QoS, I am a total beginner, so some things might be quiet obvious.

I've been looking into QoS for a few days now, and I ended up with a few questions:
1. If i want to limit downloading in Astaro, should I put a rule on the Internal Interface?
because from everything I read about Astaro's QoS, the rule has to be set on the last ASG-interface the traffic "passes"(downloadlimit on LAN, upload limit on WAN)

2. Is t here a way to calculate the bandwidth per protocol?
I know I can spend max. 90% of my bandwith,
is that the uplink, downlink, or the total of those 2?
90% of bandwith means max: 27650 kbit up, 30720 kbit down(this is 90% of each "direction" on the WAN interface)

some general info: I am using an self-built box with the latest software-version (9.004-34),
behind it, we've got 3 laptops, 5 or 6 desktops, and sometimes some VM's with Windows XP(compability),

I planned on using 9 or 10 QoS selectors, listed below, in order of the priority we give them

DNS, NTP - application selector
Games - traffic selector
VOIP, online video - application selector
http/https -traffic selector
Mail POP, SMTP, IMAP - application selector
IRC/Chat/Messengers - application selector
File Uploads/Downloads (HTTP) (FTP) - application selector
File Transfer(incl. P2P) - application selector
Others - undefined, can use all unused bandwith