Sounds as if someone is going to be busy!
For leaves: I'd make a ring of chicken-wire/mesh of about 1.5m diameter and simply plonk them in there. You could do several. With a layer of cardboard on the top and a few bricks or fallen timber to keep everything where you want it = job done.
Advantage - quick, easy to fill and empty, easy to move when they've done their job or you need to re-site them. In-between trees in or out of the sun would do.
Improving the soil structure: Double dig is the way to go as mumofstig says. Slow going but enjoyable if you don't try to rush it... Breaks up the lower levels, lets in air and gives the worms a chance. Plonk in any green vegetable matter apart from weed roots that might make their way back up again.
You could even drop some of those not yet decayed leaves deep down in the bottom.... eventually (over the years) you'll dig and turn them back up to the surface but they'll be nicely decayed by then. Grass mowings - compost them first or plonk in as you dig late autumn.
After Year 1 you will have compost bins / heaps to empty and contents to dig in.
To start with... pick a bit of a patch, skim the top and have a go at double-digging a patch so you can plonk in a few runner beans or beetroot and a few tatties. Easy crops and something to get you started while you get to know the site well and plan for the future. Herbs from seed can be useful too.
Experiment.
That's what I'd want to do......... get stuck in 1st season and learn from my mistakes - I'm particularly good at those
![laugh :lol:](https://chat.allotment-garden.org/Smileys/green/laugh.gif)
Wishing you loads of luck and even more pleasure.