Don't worry too much about the differences between flying in the US and the UK, and the charts, you'll pick it up pretty quick. I did my JAA PPL in California last year, and to be honest there's not much difference flying in the US to the UK, the charts look a bit different, the airspace has different letters, and the US tends to be more GA friendly ! (You won't find any nice flight following here in the UK, and doubtful if you'll get up above 4000'...oh and the cost!)
Shame you have to come and join the wonderful world of JAA, if I were you I'd be tempted to forget the JAA route and go the FAA route, where you can get the CPL ME IR added on to your PPL for around £10,000 as opposed to the odd £30 grand the JAA one will cost you !
Good luck !
PS You can still fly on your FAA PPL in the UK without converting it to JAA...