Hi
1) I would like to know if its difficult to use wxHaskell and STM side by side and if there are any issues I need to know about.
I have no idea about wxHaskell and STM, but I found out that hard way that Gtk2Hs + threads = bad idea. Depending on the machine I used, I got a wide class of unrepeatable behaviour, and (really) poor performance. You might find wxHaskell doesn't suffer from these problems, but I don't know.
3) How portable is Haskell? We like to run our application on Mac, Windows and Linux. The Haskell compiler (GHC) is very portable, and runs on Mac/Windows and most common Linux architectures. wxHaskell does those 3 platforms as well. Haskell tends to be very portable. Some of the more advanced features on some of the less common platforms are sometimes a bit buggy or untested - but usually there are people who are willing to work and fix any issues you run into.
Thanks, and good luck Neil