google or FB 'van life' insane endless ideas....
you want:
'walk in' so that's min 19000 internal height...taller the better (not an abundance of vans at that height) a lot are the 'mid height'
ideal internal length around 3500mm, if you can extra long 4000+ even better!
That gives you room for a 'garage at the back' bed on top...this is popular option in the states where they store mountain bikes or even Mx bikes under on slide out's for easy access...normally an external shower or hose/wash system bed on top with ceiling corner cupboards.
The section behind the Cabin effectively becomes your kitchen / lounge area, 'pull out kitchens/cook areas' are gold ...check out 'Drifta.com.au' for pull out kitchens.
With the bigger vans they normally have a bigger payload of close to 2T also...the mid size vans are normally limited to low to mid k's
Mid size - Ducato good option 2T
Large - Iveco (almost truck like!) - Merc
there's a few ideas on my Pintrest site
www.pinterest.com.au/mjonescfsp/campervan/happy van life!