I’m sure you’ll be fine. We treated ourselves to Zircon Emblem last year which is similar to other boats WRC have for hire, and didn’t regret it. With 3 to 4 hours cruising per day you should be fine, batteries well charged up. And it’s easy to cruise for that number of hours on the southern rivers. The yard will show you how the electric hookup works on handover. You need £1 cards which they probably sell and it’s very straightforward. But you don’t have to use it and not all moorings have it. You certainly don’t want to be running your week around finding it.
I’m sure you deserve the treat and it will be fine.