Alan, those are very good questions. I'm thinking about doing an Sd.Kfz.7/1 or 7/2 (
Vierling and 3.7cm respectively), but don't know if Trumpeter will be extending this line anytime soon (no announcement so far, but we know how they got a lot of mileage out of their KV-1 series). If they don't issue a 7/1 or (preferably) 7/2, I likely would go the "kit bashing" route with a Tamiya.
Knowing my perfectionism, I would add the Eduard PE upgrade for either vehicle (35183 for the 7/1 and 35489 for the 7/2). An upgrade of either gun is probably also a good idea, but I don't have any in particular in mind.
The body/chassis of the three vehicles was, from all I can tell, essentially the same (the principal differences being the FLAK vehicles had armor plating on their engine compartments and front cabs). I don't know how well the Tamiya cab and gun platforms would fit onto the Trumpeter body, but it's worth a stab.
The tracks are, in my opinion, the equal of ModelKasten's. They even imitate the dark russet plastic of MK. The Trumpeter plastic is softer, so I've had a bit of a problem keeping long skeins of the tracks from separating. But they definitely "trump" Magic Tracks in terms of performance and action (sorry, couldn't resist that pun, given all the arguing over who's better, DML or Trumpeter, with some folks refusing to buy this kit until they can compare it with the DML announced version).
As for Friulmodel tracks, they are my favorites, since they sag like real tracks, but you're adding another $35-$50 if you go that route.
The sprockets on the Tamiya (and Modelkasten) are inaccurate (too big for the former and wrong number of teeth for the latter). The front tires on the Trumpeter are post-war, but you can pick up nice AM versions from Tank Workshop ($5) and R&J Enterprises ($7 in regular, sand and snow versions).
The key issue here is how well the Tamiya cab and gun platform (with or w/o PE upgrades) will adapt to the Trumpeter body. You can consult my build log on the Trumpeter (see below) to look at how the chassis, cab and body come together, then judge for yourself how the Tamiya would adapt to it.
https://armorama.kitmaker.net/forums/121900&page=2