I converted a 2012 that looked exactly like that (minus the barn door windows) a few years ago.
Have not yet got around to posting pics but I will.
Lots of shorter trips throughout the Appalacian/Allegheny mountains but a month in the deep southwest and a week in Key west (stealth), couldnt be happier with it!
The ventilation issue is not a big deal at all. Tilt-out windows are cheap at junkyards and a power vent on the roof get the flow right across you when you sleep (if your bed is built in the typical rear area). I generally leave the barn doors open when weather permits anyway with magnet attached bug screens on all openings.
I had SO much fun building mine - like a kid building his dream fort.
Really dont know how much I spent - many things repurposed, the expensive things that stand out were; Roof vent, secondary deep cell battery, propane water heater.
Definetly check out Black'95s posts! Great ideas and detailede documentation on everything! And a very nice guy willing to help through PMs.

 

I finally posted a few pics of mine to "my albums". Give be a shout if you'd like - I may be able to give you some insite into what worked well and what I'd do different in order to help with your build.

 

Newbie here! We used a quick and affordable tnt vans kit for our conversion and have been really happy with it!