From many places souls have been called to the Vale. What is this place? How did did you get here? Why? All things you will have to find an aswers to that, along with the others you find yourself with.
Systemicly this will be an interesting turn. Each character will have two levels, one will be Fantasy the other Modern system. Depending on what you do, you will gain xp on one side or the other. There also will be general XP awarded to players, to use for what ever they like. That is eather XP tree, or to make XP payments for crafting or spells ect. You will start out only one one side of the tree. Around lets say 7th level?
As for where yourt character will come from, well any setting you can make work will be fine. From Aber Toril to Shadowruns Seattle, and far far beyond. The more interesting the Mytho's behind the character the better in my book, but what ever you can work out systemicly