Planning a project that will use a steel frame and aluminum stem and seat post. Wondering if there is anything I should do or a product I could use to avoid the problem of posts and stems getting stuck.

Yes. A light coating of grease. Or, better yet, a light smear of anti-sieze compound. But I use very light coating of grease. Or, more likely, nothing at all and just check them from time to time.

Grease