Welcome
@TalkingTeddy 
Let me try to get you started. Other folks will jump in with helpful advice.
Almost all the answers you seek depend on what you want to do with your greenhouse. So, let us know what your goals are for your greenhouse. And let us know what kind of greenhouse you have or want to have. You might also read the garden.org greenhouse forum for a lot of different greenhouse ideas and information.
https://garden.org/forums/view...
Watering, types of soil, fertilizer and trays vs. containers are going to depend on what you want to grow. Let us know.
Eggshells and coffee grounds are OK for gardens, but you'll want to compost them first. So you should start a compost pile.
Protection from frost is a major reason for having a greenhouse. How much frost it will withstand will depend on what kind of greenhouse you build and how you equip it. Do you want vegetables year-round or just an extended gardening season? You should also know that because greenhouses are so good at holding heat, they can have problems being too hot during the summer months. You will need to plan on how you will keep it cool, usually through ventilation and shading.
Dirt never goes bad! It's wonderful like that. But you will want to enhance it yearly with compost, manure and other goodies.
I'm looking forward to your answers.
