Hmm.... I'd go with tulips. Roses are nice, but since you're just getting to know her maybe tulips would be better. A nice multi colored bunch. Plus they're less expensive
But if you're going to go with roses, I'd go with a few yellow. 6-12. Nothing less than 6, and nothing more than a dozen.
I've only gotten flowers from a guy once. My ex sort of forgot Valentines day, went to the grocery store and got a rose. It was pretty much dead when I got it.