Hi -I was a 100% indoors runner for about 2 years, and I've successfully trained for a first marathon primarily on tready, but have now taken to the streets, as it's so much nicer- I'll still revert to tready for speed interval sesions, or if it's pi$$ing rain outside.
I always put tready to 1% incline. I bought a Garmin for outdoors running- it is the best way I could come up with to pace myself, and I have slowly built up my outdoors distances- it takes a bit of getting used to ,but you'll get there- and on a day like this, it's a crime to be indoors!