Stringer:
So question is, can I do 1 + 3 and drive the horse box (not for reward)? Then then if I wanted to drive commercially do I have to do the 35hrs right away or do I have 5 years to do it?
35 hours can be done at anytime you like - now or in 20 years time
What size horsebox is it - LGV C1 or C 
If LGV C then you will be under full eu regs so if say working mon to fri in a non driving job then you can only drive the LGV C for one day every other weekend due to weekly rest laws