Would you attach or copy/paste the "engine/ispcp-dmn-mngr.rej" file so I can have a look at it?
The patch rejects are probably due to white space or the fact that my ispcp-dmn-mngr has other things boiling in it and I'm currently working on a merged svn source (or I can switch to pure trunk and try to patch myself). Can you try to apply with a bigger fuzz like -F 3 or 4 ?
On the other points you raise I mostly agree. MX vs A relay might be usefull (but I've never used MX yet).
The aliases mappings might be usefull too (I'm not sure they're used but I guess so) to tweak some incoming addresses on the server.
I prefer to add reject_unverified_recipients by hand. It would be nice to be able to do it on a per-domain basis (is this possible in postfix)?
The admin templates can be changed too. Not done yet as it's another feature I never use. I normally make a reseller for myself too.
Happy to see that the patch looks OK as I tried to keep is as clean as possible.
Added: I can confirm that my ispcp-dmn-mngr has quite a few white-space issues compared to the trunk (remainings from the beautifying patch). I'll have to fix them before resubmitting a new patch