I know OT is a unique field, but I've always been taught to let your resume and character sell you, not your attire. I wouldn't take chances...go a little overboard rather than take a chance if you need to. Wear the tie for business casual. Wear the longer skirt or suit pants. Choose greys and muted solids like blues or white.
I asked the advice of a consultant at a local store for business attire. He said to imagine working in the most formal setting and build from there. You wouldn't see all-blacks, louder colors, or patterns in a hospital or SNF. Other than settings with scrubs, you would see muted solids like blues, softer yellows for accents, and greys with some whites as a foundation.
Like I said, when in doubt, I always overdress a little and leave nothing to chance. With success, you will only have to do this once, so don't take risks!