Mike,
You say that you need to 'build' 150hrs (pre-FI course.)
If I was in your position, I would build a bit of experience and spread my wings a bit.
I would first fly 50hrs in the USA. Pick the part of the country that you most want to see (hint: most of Florida is pretty flat, featureless and dull to look at from the air) and target a school that will give you a decent block rate. I would then go to either South Africa, Australia or New Zealand. Find another school and fly a further 50hrs. Then I'd return to the UK and fly the final 50hrs at whichever school you would want to do the FIC at.
The international travel could be done in either two separate trips or on a single 'round the world' ticket. In terms of paperwork, you should only need PPL validations for each of the countries. Also for the States, the visa issue should be much more simple - you aren't doing any training so a visa waiver should suffice.
If you are intending on going down the FI route, any IR training at this stage will be bit of a waste of effort and funds. Plan to complete an IR course in about 30 months time (ie before your 36 months ATPL validity expires.)
HTH.