Speedy and Roving

Do the speed bonuses granted by the Speedy feat and the Roving class feature stack?  So if you were a human your speed would now be 50 feet.

Yes, with the caveat that Roving only applies when you're not wearing heavy armor, while Speedy applies at all times.

So, in your example, your speed would be 50 feet, but would drop to 40 if you put on heavy armor.

Yes, they stack since their sources are different.

Then cast "Longstrider" for 10 more feet of movement or the "Ashardalon's Stride" spell.

Awesome, thanks