I'm old.... not new at all.
I'd start at the beginning - with the soil - leave the shed until winter when everything else is done unless the roof leaks like mad then a cheap blue "canvas" from B&Q will cure that for now.
If you can chop or strim the tops from all the weeds to prevent them from spreading seeds on your plot and your neighbours... you'll quickly gain some friends and save yourself a bit of extra work later.
Next decide on one crop for right now (you need an incentive and to enjoy success in growing something) then pick one patch and clear it for your first crop/s.
Once you've cleared and planted this bit take a look around the plot and see if there's anything worth preserving such as any fruit bushes or plants that might crop this year.... if there are give them a quick (unfussy) tidy up to keep them going.
Now you can plod your way through clearing a section at a time... either a strip or a block which ever you find easiest.
If the soil is damp and the ground not too rock hard "skimming" the surface with a sharp spade will help remove the vegitation and you can see the soil to dig it looking out for weed roots such as dandelion and buttercup (as well as any stringy and white roots) as these will regrow left in the soil.
I found taking a few snaps with a camera is useful... saved to HD and dated helps to form a diary of your progress and you can look back and see what you've achieved.
You'll have right through to spring to clear the soil - as you go along your first crop will need a bit of tender loving care and should bring you your first pay-back-crop.
By end of summer / early autumn you will have a space for Japanese onion sets - stick in a row and leave them to over-winter. Garlic and elephant garlic can be grown the same way.
While all the getting ready and clearing for next season is going on you could take a break and sort out a compost heap - annual weeds into this will give you compost to improve the soil in 12 months time - other weeds, once they have dried out a little across the plot, can be piled up for a bonfire one evening near dusk (check your site rules on bonfires first).
At home, or in the shed, sit and begin your Christmas pressie list.... others will be pleased to have some help deciding what to buy for you... include cheaper items like string, packets of named seeds and also some more expensive tools that would be useful........
I wish you as much enjoyment as I had when I first took over my plot.... take it easy... you'll get out what you put in as well as some fresh air and good friends.
Keep at it & good luck!