A couple of trips and you’ll begin to get a feel for ‘the necessities’
I would however mention ‘Security’ …. we opted for a Safelock for the spare wheel (from forum shop) historically the spares were very ‘nickable’
Also a Steering wheel lock from Halfords, we got the Safelock Pro ( our van is T6, so check fit) I know this is mostly for visual deterrent but it’s just another barrier too.
Collapsible basin is useful to carry washing up when on sites and folds nicely to minimise space. Also very popular is the foldable kettle.
All the other ‘bigger purchases’ have lots of advice and debate on this forum eg ‘Porta potti’, Awnings, Waterproof seat covers, etc.
Welcome and enjoy.