I've been using backing tracks since 1984 so possibly I can help, I also bough Home studio last year as I was planing on using the playlist feature and yes, Home studio is all you really need. My gut feeling is it would be the most stable of Sonars. You can add lots of 3rd part VST's to beef it up. Keep an eye on the Deals forum here. And it's all you need to creat what your thinking.
I originally used an Atari playing midi sequences. Those drove various rack sound modules.
As it was mostly drums and bass with the odd keyboard part I had no problem with the balance between the instruments. I had a system to keep this the same song to song. So for the last 20+ years I've been just using stereo backing tracks.
I put everything on Mini disk for a decade and then about 2004 bought a laptop. I have used Win Amp to play my stereo wave files ever since. It's the only play that will stop after each song. The only reason I want to try to use Sonar is I miss having Midi control my effects.
I've been messing with the Playlist but compaired to the simplicity of using Win Amp I find the Playlist a bit to clunky and slow. With win amp I can make set lists and easily change them on my breaks. I'm working on the Playlist project and It means totally re seting up the projects a certain way. Taking me a year so far!
Here's a simple solution if all your needing is Keyboards and a click track for a few songs. I play in a acoustic duo and I split the stereo into Bass on the left and the drums on the Right. We run the Bass to a Bass amp and it's like having a real bass player on stage. The drums go to a floor wedge that the audience doesn't really hear. It helps us keep in time. You could do the same only send the Keyboard to the FOH and the drums ( click) to the drummers floor wedge or in ears. So yes you could do this with a Tablet. I'd recomend the Radial Trim Two for this. It's perfect as it has it's own level control.
http://www.radialeng.com/trimtwo.php
So you