The problem is with OLCI and distance learning, is that you are expected to read the theory they send to you. From that you will have a million questions, trust me
It takes a lot of motivation and organisation to keep going on these kind of setups. The practical days are good, but very expensive. Praticularly if you need to go back and do it again.
Best bet is to go with a college, or do a short course. then get plumbing during the day whilst getting on with your night course at college for your 6129.
Assessors rates are anything from 150-250 per day. Take that from a qualified assessor
Keep us informed mate - good luck!!