Do I need to assemble this or does it ship ready to use?

Assembly is required. Shelves and frame ship flat and bolt together—basic hand tools and about an hour are all you need to get it standing and loaded.

Will the powdercoat hold up if I'm constantly moving oily parts in and out?

Yes. Powdercoat is tougher than paint and resists oil and solvents well. Wipe down spills when they happen and it'll stay looking sharp for years in an active shop.

What weight can each shelf handle?

Weight capacity is not specified in the product data. Contact support with your load requirements and they'll confirm whether this unit matches your needs, or recommend a heavier-duty option if you're storing engine blocks or stacks of wheels.