Welcome to the forum
The first thing is to check what the rules are for your site - there are often limitations on what you can have on your plot e.g. no sheds, or max two structures, of certain sizes.
The usual size of shed is 6' x 8' I find - you don't want to take up too much space. Greenhouses again often 8' x 6' or 10' x 8'.
Greenhouses - you will need to choose between glass, toughened safety glass, and polycarbonate (twin-walled or single). Consider whether it's a locked site, how much vandalism, how windy.
Siting of the structure - don't place it where it will cast shade on your plot or, more importantly, your neighbour's plot. Site secretaries here have to approve the siting before a structure is erected, in order to provide some consistency of approach and to protect everyone's growing conditions as much as possible.
Fruit cages - to be honest, I'd wait and see for those. Many people grow fruit under netting that is suspended from canes with yogurt pots on top. You don't have to get it all sorted in year one, particularly as you're talking about considerable expense with your list of items.
