If you owned a greenhouse, what would you grow?

A few questions here. First off, what can be grown and what would you grow in a greenhouse? Flowers? Vegetables? I know nothing about greenhouses and need some advice.

The house is approximately 300 square feet with operational ceiling and wall vents. 10’ wide x 30’ long with two strips of dirt flooring running down the length about 3’ wide. A concrete walk runs down the middle and venting cranks located in the middle. It is empty with no shelves or racks.

Though vented, there are no fans. I don’t even know if forced ventilation is needed, but the house is very old so this would require installation. Recommendations?

Can the existing dirt floor be used, or should new earth be installed?

Does one install tables, shelves, racks for multi-level growing? If so, how would the sunlight get to the grounded plants? What type of plants would grow in pots on shelves, and what grows best in the ground?

Also, it is missing a few glass panels. Can they be replaced with plexi-glass or does this require real glass?