The hardest thing about sweep tapping in my opinion is getting your fretting hand in the right place at speed - you have to sweep the arp diagonally across the strings so you're ready to tap, tap the right notes, and then sweep back down again diagonally in reverse.

I personally found getting back down again to be the tricky bit. For practice, sweep any 5 string minor arpeggio, and to start with just tap a third on top of it and come back down. Then you can move to double tapping or tapping more than one note once you've got the bones of the technique down.

And on Oziel - I think I like 'Isabella' the best... cool melody and not too tricky until later in the piece. The sweep tapping he does isn't actually that involved, but the speed makes it sound very difficult...