Here you see my (probably highly inefficient) solution to the problem of making an entire coat out of lots of little pieces. It involves a lot of 'singles' i.e. hexes which aren't made into flowers, including some 'fourers' on either side of the central back flower, but I think it works.
The diagram above shows the back of the coat (laid flat) at the bottom, and the front wings at the top. The black line represents the shoulder 'seam'. On either side of this seam, coloured flowers in the bottom half are matched by ghostly flowers in the top half - these correspond to each other and show where the two pieces should be joined at the sides. For example, the green flower on the right of the back piece should join to the yellow and grey flowers at the front in the way shown.
The colours are chosen for ease of diagramming, not representing either your attempt or mine! I managed to slightly co-ordinate my flowers so that the hotter colours were at the top and the cooler colours at the edges.
Once I'd stitched all of this together, side-seams and all, I could wear it - and in fact had been doing so intermittently to check the length for a while. You could easily make it longer by adding more flowers or singles to the bottom edges; I personally was getting impatient at this point and started on the next stage, which is taking all the paper out. I left in the papers at the edges of the garment so as to make sewing in the lining and sleeves easier, but the rest I removed. It's lovely to see the colours pure and unsullied by tacking stitches, and very easy to yank out said tacking in an afternoon. SAVE THE PAPERS. If you ever want to patchwork again you will save yourself a lot of bother if you already have all your templates handy.
When I have the time I shall look through the scraps my grandmother gave me and see if there are any pieces big enough to make a lining out of, or sleeves. I'd like the sleeves to be slitted with poppers so that I can easily roll them up to wash up in. Watch this space...