Sounds like you’re well on your way. It would be worth clarifying what you are aiming for, to determine whether you want a leisure battery, whether you’re looking for a full conversion, with cooking and a fridge, heater etc? What charger will you require? Mine used to have a basic ‘split charge’ relay which is useless with a ‘smart’ alternator, so I pulled that out, and installed a CTEK 250SA and have been very pleased with it.
The lights require a suitably rated and fused positive connection and a decent earth. If these are touch lights, the switching is dealt with by the unit, if not, they’ll need to be switched too.
If they’re off the starter battery, consideration must be made to over discharging the starter battery and not being able to start the van, although a few of these are very low current.