I think there are also some general decisions on how ISPConfig works, to make the next release moe scalable with support for multiple servers in one controlpanel, virtual mailusers etc. Ive posted my ideas here:
I will have a look at the feature lists from cpanel and ensm. I think directadmin is also quite popular the in the last year:
What do you prefer, an navigation on the left for the different functions like adding users etc. or the style of cpanel wit icons in the middle of the page?