Other than a 'trial flight' in the UK, to check I was going to enjoy it as much as I hoped, I did all the flying training in Florida. But before leaving the UK I did all of the exams except for R/T and Nav. Could have done Nav as well but thought that it would make more sense having some practical experience first before the exam, whereas the other subjects seemed better (for me anyway) to have the knowledge before needing to put it into practice. So I studied Nav and R/T before leaving but took those exams in Florida.
I would certainly not recommend anyone trying to cram in all the training plus study whilst abroad. I was there four weeks (training for three plus a week holiday) and there's no way I could have managed it all. There might have (just about) been time for it but it would have been too much of a demand on my brain cell for me to cope....
As englishal and scottish_PPL say, definately better to be at least ready to take the exams with the subjects all read and understood before leaving the UK.
Scottish_PPL also makes another good suggestion about starting a relationship with a local flying club now. I'm sure you will find the UK totally different to the US, and you'll probably need more than just the hour or so check-ride with an instructor when you return. Before leaving for Florida I explained to the local club CFI what I was going to do, took my ground exams there, and made it clear that I wanted a few hours with an instructor upon my return to get used to the UK differences (R/T, overhead joins, much more restricted airspace etc). That at least reassured the CFI that I was under no illusions it would be all plane-sailing (pardon the spelling-pun).
April should be a good month to be in FL - that's when I was there and it can be hot and thundery but not as much as in high summer! We had a few tornado warnings when I was there, so don't always assume perfect weather will be the order of the day. My entire first day was washed out with thunderstorms. Flying early in the morning was beautiful (apart from when the viz was poor) - generally very still air, much cooler and less turbulent. Not so late afternoon - it can be bumpy. The most important piece of advise is to have have fun. Good luck!