Your starter battery neutral will be the vehicle body shell so that's one crimp lug out of the way.
Your starter battery live will already be under one of the front seats so add a fuse holder and fuse there to extend that to your Victron.
The leisure battery pair to my Roamer are big arse crimp lugs to bolt on terminals but this is via the battery isolator which may well be screw or crimp lugs terminals depending what you get.
Get a pair of those small manual crimpers with the blue plastic handles that are on Amazon/eBay and have adjustable wheels either side to crimp from 10mm2 up to 70mm2 lugs, get your lugs from the nearest electrical wholesaler and figure out which size bolt hole will suit you so say a 25mm2 crimp lugs with an 8mm hole.