I walked every step of my first sprint tri. No problem.

If your swimsuit is really comfortable and you love it, can ride in it and walk/run in it, go for it.

I don't actually own a swimsuit...

I swim in a black sports bra and black UnderArmor compression shorts. (I need more support than a swimsuit could give me, anyway. And I'm very uncomfortable about showing my butt and thighs.) I add bike shorts with an attached wrap skirt for the bike and the walk, and put on a tank top.

Lots of people like tri-shorts, which are like bike shorts but with a thinner/smaller chamois. You wear those thru the entire tri, don't have to change or add anything. There are also tri-tops, which are bra-tops with pockets in back. Tri-suits are one-piece combos of shorts and top.