The 50 is open and roomy plus gives you a lot of space to store stuff under and on the bed. But a walk thru model gives you access to the rear w/o having to go outside to open the rear doors. Most Voyager type tops have walk-thru type builds and those have a lot of overhead storage. As a big guy I feel cramped in a walk through Ford but the cutaway is a bit larger and depending on your combined size, the larger penthouse might be OK for two when sleeping up top. Maybe installing a Colorado Camper Van top on a used vehicle is worth a look-see.They have roomy space up top.
It seems to me if you're after a van that holds a couple of dirt bikes, finding a fully constructed build specific to your needs might be difficult to find used. SMB will add a top to a used vehicle in most cases but I haven't heard if they will do an interior build out on one...in the past they didn't.
Yeah lots of options. Do you really want to haul bikes inside? If I were building a vehicle to haul light motorcycles inside I'd be looking at a pop top with storage in the rear, a small galley with fridge, potable water tank/outside shower and a couple of swivel chairs so you can relax inside out of the weather.
If you frequent hotter weather and you want air conditioning, the larger vehicles are outfitted better for that. Just depends on what you really want or need. You can almost fit into anything depending how tight you want to make it.