Thank you for all the hints and tips guys, it has changed a fair amount of what I was thinking.
First one is tethering. I do not plan to tether, but will have a harness on under the life jackets, which will remain foam. I initially thought putting them on the (now know as) suicide seat would be good as I could keep an eye on them all, but will change the plan and look to go for a bench seat arrangement at the back.
It wont just be family based rib fun going on, but having the incentive to go more steady to start with wont be a bad thing. I have seen and got into plenty of trouble at 8 knts so taking a steady approach to it is going to be no bad thing.
I've done some training already, but like with a driving license it is enough to get me to a point where I recon I can start learning.
Cruising will initially be south coast based and I did think about a bit of time on the Severn from Portishead, which is only about 40 mins away from me.
One day it will be mine. Oh yes, it will be mine