Hi Craig, and welcome.
Obviously I dopn't know your dertailed needs, but here are some general tips which apply to all of us.
From your reading of PMH (and maybe even other mags!
), and your knowledge of your own travelling companions, you need to draw up a list of features your van MUST have, and those you'd quite like if possible. Then as you go round dealers etc, be single-minded in rejecting anything which doesn't have all your "musts" - however attractive it may be!
If that leaves you with no options at all, ONLY THEN look again at your list and downgrade some of the "musts" to "prefers!"
You don't mention whether your six berths include one for a wife or girlfriend, but if so make sure she is involved when you draw up that list, because you both need to "own" it. Otherwise you'll end up arguing in front of the dealer about whether that payload really IS essential, or whether it can be sacrificed because this van has just the right colour upholstery.
And before anyone accuses me of sexism for that, it's purely that it's Craig who's asked the question. If his partner (M or F - no homophobia either!) had posted, I'd be urging THEM not to be sidetracked by CRAIG'S taste in decor!
Once you're pretty sure you've seen your dream motorhome, haggle about the price on the windscreen first, THEN about any part-exchange (I know it's your first van, but some people trade in their second car). FINALLY, start specifying any extras, and additional work you want done before delivery. Directing the negotiation in that order ensures you know exactly what you're paying (and receiving) for what, as it stops the salesperson from offsetting one thing against another.
That last paragraph sounds rather cynical. In fact, most of the salespeople you'll meet will be keen to look after you. But they have to turn a profit, and you want to be sure you only contribute your fair share to that.
I'm sure I'll think of some more tips, but meanwhile I'm also sure that others on here will have some good ideas for you too.
Whatever you buy, enjoy your new lifestyle!