Hi Luke,
For the first year, your leave will be arranged for you, taken as a group at certain points in the training programme.
You will get a break between finishing your basic training (wherever that may be) and starting at the institue in Luxembourg, and then again between finishing in Luxembourg and starting at MUAC (a week).
Once you come to MUAC, you will do your "transition phase" which is roughly 3 months, (7 weeks of theory, and 4 weeks of simulator training). After this you will do your CC-OJT phase which is about 4 months, and is your first opportunity to take leave when you like (so about 12-16 months after you first start). Depending on when it is in the year, most trainees take at around 3/4 weeks in this period.
After that its back into the simulator for 3 months, which includes a scheduled weeks break at the half way point. Once you have completed that its into the ops room again for your full OJT until you complete your training, and during this time you can take leave pretty much whenever you like.
When you first start though, you will be given the dates for all of your phases of training, so very quickly you will be able to work out when your scheduled breaks will be for the first few phases.
Also, when you are in the insitute in Luxembourg, you will get various long weekends for public holidays etc, which are a good opportunity for popping home for the weekend.
Finally, as for validated controllers, off the top of my head the leave allowance is 24 days, plus 17 days in lieu of public holidays, plus days that are given based on your age, and days for going home based on the distance between MUAC and the place where you lived when you were recruited. So its around 45 days at the moment, although by the time you actually get to MUAC, this will have been reduced slightly with upcoming changes to rostering, where there will be less leave but also less working days per year.
I hope this helps, any other questions feel free to post away or send a PM.
GJ