You are now touching on the crux of why this is a bit of a tricky field.. the hardest thing to solve is " what do I need/want to do"?, and it sounds like you are on your way there..
Definately go with at least 24 track capability, and don't forget returns.. ( headphone mixes, etc) Take a good hard look at the type of places you will need to get the rig, if we are talking backwoods barns and stuff, your chassis requirements will be very diffrent than doing mostly urban work..
does it need to be surround capable? and video requirements? Storage needs? Climate controls? Sleeper?
It can get a bit tricky to get actual design advise, but there are very reasonable options out there who do great work. PM me if you want a lead ( and no, it is not me
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