I'm currently operating 20+ current accounts and 10+ Regular Savers
I use a mix of SOs and manual payments. I used to do almost everything manually but a couple of years ago was out of the country for several weeks and didn't want to have to use insecure internet connections to shuffle money around.
All but 1 RS are fed by SO, as are their respective 'feeder' accounts where I don't keep a large balance (eg First Direct, HSBC, M&S). I also try to make say a credit card payment, or use the debit card for those accounts, just so they show some 'current account' use
I keep a very detailed spreadsheet which I update at least once a month (more like once a week) having logged into every account to make sure nothing has been missed, cream off any interest etc.
It took some detailed setting up, but could be organised to run itself.