Hey saxyman. I grew up in Kemmerer, Wyoming so I know what you mean about a lack of music stores. The only place I used to go sometimes was Summerhays music center in Salt Lake City. There was a guy there named Ernie Northway that was extremely helpful, also makes great custom mouthpieces if you're after a bright Pete Christlieb kind of sound.
It's hard to say much about the different models or sizes without just trying. And maybe that means going for something and then trying to trade it here later for a size higher or lower. I have been playing Wanne's pieces on soprano and bari for some time but just got a Gaia metal 10 on tenor. I think it's fantastic, at least as good as my main piece which is a Frank Wells customized Florida Link. It's also a bit darker than my link, and probably about as dark as I would want to go. I'd say, if you really want the darkest sound possible than the Ambika could be a great choice. I did try one a while back in wood and it wasn't so far from the Gaia metal I had to compare it to, but there was a difference. But if you want a tad more versatility, perhaps the Gaia is a good bet.
It terms of size, that's very personal. However, I've found all Wanne's pieces play so easily, for me they feel one size smaller than they are. In fact I got a great deal on this Gaia 10 because the owner felt it was too small (not a common reaction for sure). I was even considering getting it opened up a little, though it plays so well I think I'll wait a few months and see how I feel. What size is your Kessler? If it has a smaller chamber you may need a bit more air for either of these pieces. Generally a 7 is a very standard tip and one that would probably be easy to trade if you wanted to get something bigger later. Really depends what you're after. Also, I'd bet during your trial you could get a pretty good idea how the size suits you and Matt, I'm guessing, would be able to swap pieces if need be.
Hope this is somewhat useful, good luck!