I have answered all your questions as following :-
1) Does each
website hosting get it's separate control panel, or are the domains held as Addon Domains, as subdomains of a master one?
Ans :- You can create separate cpanel accounts for all your customers and they can then add addon domains / parked domains / subdomains from respective control panel. If you cannot give cpanel access to your customers then there wont be any difference between shared hosting and reseller hosting.
2) Do I have to buy Domains off eUKHost, or can I simply point them towards your nameservers?
Ans :- You can simply point them to nameservers assigned to respective server or you can register your private nameservers and ask your customers to point their domains to your private nameservers.
3) I tried calling your 0800 number to ask these questions about 5 minutes ago, and got no reply. There was also no reply at 10am this morning, and no reply last night. Is this representative of your phone support, or was I calling the wrong number? 0800 097 4828, and there was no reply at all.
Ans :- I am not sure why you could not get hold of anyone on this number as our phones were ringing all the day and we have answered many calls throughout the day. You can also try other numbers listed at
http://support.eukhost.com if you don't get response from main toll free number.
4) What is your Acceptable Use Policy with regards to server resources usage, of PHP/mySQL, etc.?
Ans :- All our shared hosting servers and reseller hosting servers are running on Quad Core Xeon Servers so the CPU power or CPU cache cannot be questioned. You need to ensure than none of your accounts use more than 10% of CPU as we will need to suspend respective account which uses more than 10% CPU.