I have grown rhubarb from seed and although very satisfying it does take a few years. You can pick one or two stalks per plant in the second year. Biggest problem is that you end up with dozens of plants - rhubarb is one of these species where you seem to get 100% germination.
Unless you are growing commercially it takes over and you'll want to grow something other than rhubarb, so best to scrounge a bit from someone else.
This shouldn't be a problem - I keep hacking mine up and it seems to make no difference whatsoever to yield, but I do mulch with well rotted manure in the autumn.
On the soil issue I have to say that I would advise you to cheat and spray roundup on what you aren't going to be able to do in the next fortnight, leave it for a couple of weeks and cover it in as much manure as you can get hold of between now and winter. (6 inches absolute minimum.) You will be amazed at how much work earthworms will do for you. You can then rotovate the whole allotment in early spring and start at the right time of year. By spraying you will be killing off the weeds before they set seed which will help both the bit you have done and the remainder.
I took over an old allotment at our previous home and if you try to do it all at once it just gets on top of you and you end up doing nothing, so be realistic and enjoy a portion of your allotment whilst planning ahead. Remember it's supposed to be enjoyable and there's always another year!
PS Whatever you do don't rotovate without weedkilling first - this is known as weed propogation.