Admin Control Panel - - Go to host/settings and the choose the classic control panel I think - but sometimes this causes errors with skins that have the new control panel skinned in it.. but that is how you put the minimum one on. If you don't want people to be able to make any changes, you have start setting permissions at module level so that no control panel appears.
I can only share my experiences with hosting since I have several, including Linux... yes I own linux box too.. so I'm not a systems admin person, but have had to wear DotNetNuke problems.
In my opinion, DNN is a big hungry on resources. If you run multiportals, off the same db - eg. .children, I'm not sure you can do application pooling since they are all on one instances, so you need to have your sql fine tuned I guess to manage the requests.
In reference to whether users require ftp access. No they don't. None of my clients have ftp access. The manager works well for them, and the modules that are available for photo galleries and such really do make a difference in file uploads. Although I do tweak the web.config sometimes and think that there is a bit of site tweaking and management to make it run well.
I have my own thoughts on how servers should be run, but it's only a personal one, and not qualified to put my opinion forward, since there are many more experienced hosters here who probably wouldn't agree, and it all depends on your own circumstances and needs to get these things setup correctly to suit your business model.
Nina Meiers