I wouldn't mess around with a step mash if it's your first AG. Then again, I've never done a step mash, so...
IMO, 155 might be a little warm for an IPA. I like 152. But you don't have a ton of unfermentable sugar in your grain bill anyway. 155 will work, 152 will be a touch drier. I guess it depends on what you're shooting for.