1. Add at least 20% to the cost
2. The chances of getting hired with 150 hours are minimal. As said before insurance companies need at least 200 hours, but a lot are raising the bar to 300 hours.
3. You can do it in 6 months, but it's hard work and the school/instructor has to cooperate. (I did it in 5.5 months)
4. Building up a 1000 hours is possible, but only a very small group makes that. Basically only the people hired by HAI.
5. Don't count on it. As a CFI you make between $15 and $25 an hour. At most schools you won't be flying more than 40-60 hours a month.
6. $1500 as said before
7. There is no conversion, it's doing the JAA ATPL or CPL theoretical knowledge course which takes at least 6 months (usually a year) and then doing a number of hours flight training determined by the head of training of the FTO, usually at least 10. I know of people who needed much more.
8. As the previous poster said it's not easy to get hired because you don't have a network. The helicopter world is very small and people have to know you. If you do a JAA IR then there might be possibilities off-shore, that's probably your best bet.
In short is it worth while going to the US to do your training? Maybe, I think a better way might be to do your JAA training in the UK, and go over to thes States to do some cheap hours building and get a flight instructors rating over here and build up your hours here as an instructor.