I love Musicals but I've never seen this one! I'm a little intimidated by all the expected audience interaction (and dressing up) would I stand out if I just went without the costuming?

Not at all. My first one I went with just a meat loaf tee on and then normal attire. Plenty of others there in "normal" clothes. The audience interaction is just a few scenes where it's a bit pantomimey with audio cues. Fast forward to the last time I saw it in corset and lab coat... I'd say it's 50-50 so you're comfy however far you go!