It's an interesting sounding character. Though I might suggest creating a character that's separate from Tham. Planeswalkers aren't exactly that common of an occurrence, so having two from the same spot hanging around and doing business is a bit much. Especially with all the other references you make where everyone is seemingly aware of walkers and other worlds.
I'm not sure btw how I feel about the simic hounds Tham summoned. Most creatures and beings other than planeswalkers can't survive the BEs never mind summoned beings made from the aether.
I'm still looking for more in terms of the description of his plane. Look at the kind of summaries they do here for the various planes. For a totally new plane, that's the kind of in-depth info I'm looking for. Important people, places, mythology, etc.
I saw your post about you having a lot of Munchlax sitting around, but below you said you haven't been trading them in over a year, I was wondering what you meant by that? Sorry I have just really been looking for one as of late.