There are marinas which also have canalside moorings along the cut near the marina entrance. I'm pretty sure some of these have leccy. So you would be able to have everything you want.
As far as residential/post etc goes, tell the site owner that you're there for less than 50% of the time and they should be fine for you to be officially non-residential. In my experience, the more laid back owners are quite happy for moorers to have post delivered to their office, chandlery etc even if they're officially non-residential, so the address the bank, dvla etc have for you would be your mooring address.
The fact is that there are tons of people living unofficially in marinas and staying under-the-radar. When I asked BW for an official response to how much of the time I could be staying on my BW leisure mooring they were quite evasive and tried to suggest that I should ask my local planning dept (yeah right!) When I pressed them they gave a response that they would prefer moorers to be on their moorings for no more than "4 or 5 nights a week". Seems to me that you fall well within that.
Also bear in mind that not all marinas are big 200+ boat affairs. I moor in a basin on the Huddersfield Broad canal so we're stacked in like a marina, except there's only about 15 boats. We still have all the usual marina facilities though.