've absolutely no idea where to start, what materials I would need and what to plant, pref a mixture of flowers and vegetables
Now is the time to start planting. Seed is always cheaper than buying plants, and there is some satisfaction in seeing it coming up. You can get a cheap heat mat on E bay for under a fiver that will fit on a window sill. If you have lots of flags everywhere it might be good to plant in containers, look for things like 'The Sutton' broad bean and 'Kelvedon Wonder' peas that don't grow too big. Tomatoes and lettuce are good things to get going now in the veg dept.
Take your time planning where to take up the paving and save the flags, they come in very useful for edging beds I find, not so hospitable to slugs as wood and much more durable. It's trying to do informeda lot all at once that usually beats peop0le, a little at a time is good, and it builds surprisingly well.
A green house is useful, I just got myself an 'Outsunny' poly tunnel, much cheaper and almost as good, though it won't last as long.
Good luck and keep us informed, plenty of happy hours ahead and lots of fun new stuff to learn.
PS, go for cheap plants, they are cheap because they are easy to grow, expensive means harder to grow, not better.