IIRC, you need an M8 X 1.25 X 70MM fully threaded.
As far as your spare belt goes, the Gates belt has been given some praise of late by actual users and for a spare, you can't beat the price when purchased from Discount Fleet. The OEM is typically close to $110 while the Gates can be purchased for $35 + shipping. The Gates part # is 30G3750. Elsewhere, the Gates belt is closer to $65.
30G3750 Gates G-Force CVT Belt - Ignore the number on the picture, the number on the page itself is correct.
There are several videos of interest on youtube. One will show you how to do the belt change and includes the bolt size (he uses a slightly shorter bolt, but better to be safe than sorry on length, IMHO). Another compares the OEM belt with Dayco and Goodyear. After seeing that video, I'd avoid the Goodyear.
Best of luck, and I hope this helps some.