1) Yes and no, though due to the design, an undershirt is required to make it comfortable.
2) I find it very uncomfortable to sit with at all. I prefer a pocket holster for this.
3) It's about as comfortable as a regular IWB holster. I will say for hiking though, having slid down hills and had to crawl up mud banks, that I highly recommend a holster with good retention (i.e. not the smart carry).
4) Run? Yes. Bike? I don't prefer to use it while biking.
Mine mostly sits in the closet, unused.
This isn't incredibly discrete, but it gets the job done (for running, hiking, or biking):