I am not trying to knock all of your hard work and enthusiasm but remember if you have passed you are on a waiting list. That waiting list will contain numerous other people in the same position as yourselves. They interviewed over 400 people so you have done fantastically to get this far.
I do not know how many courses are due to be held by each service over the next year to 18 months, so I cannot help there. Also your choice of FRS is just an indicator for the recruitment team. If you have done really well, and you are within the numbers required you may ( I will say again, may) be offered a place with another FRS.
As others have found out in the past you may well have passed the interview but are not required, so you may be in a position that you have to re-apply next time. Do not get down hearted, if you want the job you will persist. The amount of people that applied was huge and lots of you have got this far, and unfortunately some will miss out even though they have passed all the assessments.
Lets hope you get offered a place, successfully pass the medical and start the hard work of the course!