He leads the league in goals the past 4 months, do whatever it takes to keep him in shooting mode.
As for linemates, Stamkos has always worked best in pair, it's just simplier and suits his game, the 3rd guy can be anybody as long as they don't try to get too involved in the play. Peak Stamkos had guys like Malone and Downie as his winger.
I wouldn't be opposed to trying Callahan with Stamkos and Miller, just because Callahan really just knows his role and won't do anything fancy, puts the onus on Stamkos and Miller to produce. I think a guy like Gourde gets too caught up in trying to create offense with Stamkos they stray away from their own strengths when on a line with him.