Welcome! I'm another TEer from Central Indiana.
Here's my differeing perspective: I sold my indoor trainer last year because I rarely used it. I found it to be incredibly boring, although there are certainly enough people who use them. Some like them, some grin and bear it. Honestly, I can't say that it mimics real riding enough that it will provide any more in the way of "practice" than a bike at the gym. You mentioned using a stationary bike. By that, do you mean you've been going to spinning classes or just using a stationary bike on your own? If it's the latter, then I'd recommend the former. I find spin classes to be much more fun than either the trainer or a regular stationary bike--but that's me.
If you decide to get a trainer, take your bike with you to one of the various shops in Indy and ask to test some out. In my experience, fluid trainers are quieter and "feel" better than magnetic trainers. But they also cost more.
As for riding outside in Indiana in the winter. It can be done, but it takes the right gear and some determination. While I hate the Monon as a general rule, it's not a bad place to ride when it's windy and cold out because it's much more deserted and the trees provide some cover from the wind.
Live with intention. Walk to the edge. Listen hard. Practice wellness. Play with abandon. Laugh. Choose with no regret. Continue to learn. Appreciate your friends. Do what you love. Live as if this is all there is.
--Mary Anne Radmacher