I use this tuning for one of my guitars. I use four octave strings, and two normal.

1 - 012
2 - 016
3 - 010
4 - 014
5 - 020
6 - 030

I experiment with guages, some - depending upon which guitar I have high strung, how it sounds, and how much risk I'm willing to take if I go heavier. You get more power out of heavier strings, and better sound (generally) but you're increasing the strain on the guitar's structure - so make changes slowly and wathc your neck. You'll see movement if you strain it too much - then back (and re-adjust your neck).

If you stay with the guages I've listed, you should have NO problems with strain. In fact, you should be able to beef it up a little.

I would go to the guitar shop and buy single strings. The bigshops all sell 'em that way. Probably 'electric' strings, but that's no diff, really. Alloys may differ some, and guage of the packages - but you're not buying packages - and the difference in tones from high stung guitar is FAR greater then the difference in alloys!

Good luck with it!