rockydog:

It would be reasonable to protect citrus with a greenhouse. I didn't say easy because that depends. I've had both potted and inground in mine. I like inground best but I have a tall greenhouse with very good heating and cooling. All you need in your location for citrus is protection for about 3 months in winter. So I'd be thinking about a greenhouse that is covered only from Nov to March. Then remove the covering for the rest of the yr. You'd need a heater in winter. A greenhouse without heat isn't much protection.

You also need ventillation even in winter for those warm spells between freezes. That means you need to have roll up sides or another means to allow lots of warm air out the top and cool air in down low.

Adding other crops is possible but if the crops have widely different needs it might be difficult. Choose your highest priority crop and design the structure around that crop.