Currently we have two sticky threads. I think it's okay, since both are currently important.
But in general: How many meta questions should have a featured tag?
1, 2 ... or maximum 3?
Use with great restraint. It's pretty rare that you actually have to 'feature' a post. The system already has processes in place to raise certain meta posts to the main Q&A. The featured tag was intended to be used for exceptional situations only, typically when timely issue comes up that are of broad involvement of the entire site.
But be careful about the temptation of slapping a featured tag on a post you simply want people to see. Every user feels their meta post is important, and with so many posts vying for attention, the ability for Moderators♦ to say their post is more important than the rest is really easy to abuse.