the card should fit fine and airflow will not be a problem as long as you organize your cables neatly.
as for SLI, the asus card's terrible for it because it's triple slot. SLI leaves no room for cool air intake for your top card and it'll heat up a lot. if you want to SLI, I recommend getting a two slot card. otherwise, I've seen plenty of people SLI or x-fire in that case