Ooh that Haimi is VERY cute, that's going on my list. Three Flavor Delight is absolutely lovely to knit; the original is done is a very expensive silk mix yarn, which I would imagine either the designer's girls have been trained to respect from an early age, or they wore it for the photo shoot and have more practical ones to wear for every day. I've done my version (really as a test run as much as anything else) is a 'ball bigger than your head' Sirdar Bonus Aran in Tudor Rose, pic of the work in progress here.
The pattern should tell you how many balls of wool to buy. Mostly if you're knitting it in the same weight of yarn (say, double knitting) it'll be a question of buying the same number of balls in the other yarn as most 50g balls of double knitting have the same total length. If you were going to use 100g balls or 'bigger than your head' style balls, you would calculate the total number of metres in the project. You just look up the pattern's yarn in Ravelry's yarn section, see what the total number of metres per ball is, then calculate the total for the project, then see what that equates to in the yarn you want to use.
Yes, you would just knit fewer rows in the sleeves to make it short sleeved. You could even make it cap sleeved, I suspect, by casting off the stitches you are meant to leave behind to pick up for the arms later, I'll have a look at the pattern. This would also make it easier to knit.
Fancy links are done like this - I'll have to leave spaces in so the post doesn't convert it to a fancy link:
Two open square brackets then name of site www.ravelry.com/ then a space and then the words you want instead of the site address Ravelry then closing square brackets
So http://www.ravelry.com/ Ravelry
(but without the space after the first set square brackets and before the second set)