I gig two of these on a regular basis, though one of the cabs has the tweeter (which I don't turn on).
1) I got my cab covers used on TB. They are the Aggie versions and work great for what they are, very durable over the year+ that I've had them. Don't have direct experience with other aftermarket brands but I imagine they are all good and of similar quality.
2) For the scenario you describe, yes, two of these is great for that type of gig. I have a DB115, that I love, to pair with a 112 should the need arise for more volume. But I've had great success with the two 112s in pretty much every situation.
3) I don't touch the ports. I have a hi-pass filter I use if I want to cut down on the super lows. In any case, I don't find these cabs super heavy on the bottom end anyways. They are punchy little bastards that sound great.
4) My gigging amp is a TH500. I think they match up great together so the TH350 would be great as well. I've used my old V4B through them and that sounds great too. I've been able to cop that V4B sound pretty well with a Walkabout. Great sound. For under $500, either of those scenarios give you great affordable tone. After that, you are just balancing cost vs. sound. Not to imply cheaper or SS is necessarily worse sounding, just that I find those solutions tonally much different than the TH or a tube head etc.
My mind is a raging torrent, flooded with rivulets of thought cascading into a waterfall of creative alternatives