My 2 cents.
You can leave off BT, GPS, 4G unless your using it & low signal can cause heat build up.
Yes streaming & charging can increase heat, as well as if cased, in your pocket, etc, but your phone should not get hot (approx 125' f is the Auto-Cut out for too Hot), my max temp in 9 months was 105 F (from data records)
Right now, on Performance Mode (always), No Data Savers, Gmail, Tweeter, Hotmail, Calendar sync always on, I have been uploading large pics to dropbox on Wifi & 3G (5 bars) for last one hour, using & charging my Photon & batt temp is 91.4 F, with TPU Case on it, indoor temp 77 F.
I have also found WiFi with Youtube is less heat then 3g or 4g.
I think 105 F is probably OK in heavy use, but everyone's environment, settings, signal strength, etc will vary results.
Hope that helps