I don't use a mobile device myself, everything on the PC.
For drums, there are quite a few good packages out there. EZDrummer, PC Drummer Pro, Steiberg's Groove Agent 3, and the list goes on. Even one called Hydrogen on SourceForge. Lots of people use EZDrummer, though I prefer PC Drummer Pro (though it's a toss up).
Mainly, though, I use the drum systems in Reason most of the time. I just like Reason for everything.
For bass, I either use a good bass synth and the keyboard, or I program bass samples into the drum systems and let it handle everything.
As you say, there's lots to take in, and everything depends on where you want to go and who is helping you. Everyone will suggest something different...