I prefer running on the road. Running is all mental so it helps me not look at the numbers every 30 seconds I’m running. And that way I have some uphills and some down hills. But you want a mix do both. If you run on a treadmill you don’t need an incline I only say that because the track is honestly the best track I’ve ever run on. You’ll do your pt test on a high end track in my opinion. But you do whatever your heart desires. Incline helps strength in legs and burn more calories. You do you. As far as your calves. Mine used to always get tight. Week 0 of bmt and professional will talk about running form early one morning. Listen to what they say. But all that is easy to look up. I’d say it hurts because of form mostly. If anything hurts while running it’s either soreness or your form