Nexus 7/Android "Must Have" Apps

I have a question about playing ‘music’ on one of these devices.

Is there a way to play more than one track at a time.

I am the ‘stage manager’ for a lot of plays. It would be useful to be able to play a very long rain sound. (one that lasted for a hour) and then occasionally (on cue) hit a thunder sound.

Is that possible on a tablet? What would let me do that?

The apps that get used most on my Nexus are:

Astronomy- Google Sky and Sky Safari. Take it outside and point and you will never look at the sky the same way again.

Simple classic games that have stood the test of time: Angry Birds, Subway Surfer, Temple Run, Where is my Water, Cut the Rope, Sprinkle, Vector, Riptide GP

Kid stuff- Any Lego, Duplo, or Dr. Panda game, Toy Story Smash it

I just got an android tablet. Can someone recommend a word processing ap that has the function of predicting what words you’re going to type out? I’m finding the keyboard it came with frustrating, and I wouldn’t mind auto-complete like my old pocket PC’s version of MS Word.

I’m fairly sure that the keyboard function is independent of any individual app. In that case I highly recommend Swiftkey, it is remarkably good at predicting your next word. It’s worth paying the small fee, and also worth letting it scan your emails and texts to familiarise itself with your vocabulary.