Portmans has some great stuff out, and Target has some nice houndstooth stuff and berry shirts that look fabulous together IMO.
For your hair, I'd do it in a bun or a nice sleek ponytail. I don't like plaits, I think they're a bit dated.
The liner - it depends on how you plan to do it. A sleek, thin black liquid line, then yes. Smudgy pencil liner surrounding most of your eye... then no. I'd use nude/taupe shadows, natural peachy cheeks and a fairly plain lip.
Here's some things I think are great for an office job!
I think don't be afraid to wear colour, ESPECIALLY to an interview. I think it will make you easier to remember. "That woman in the beautiful blue dress," rather than the standard boring black-and-white combo.