Hi Tim!
Firstly, Welcome to the wonderful, but very addictive "World of Gardening" 
Sound advice above, and pretty new to allotmenteering myself , (Got our's March last year) and as previously mentioned, your fellow allotmenteer's are almost overwhelmed to pass on advice/knowledge!
A shed is a must have, if only for somewhere to duck out of the rain, n Jeez, as we all know only too well, we had enough of that last season. 
And one inspirational piece of advice I was given by a fellow allotmenteer was, Once you have cleared the ground, knock up a few raised beds, even if not for a permanent fixture, and plant it with veg you like to eat, as it will act as a little reward for all your hard work come harvest time and so help you becoming disheartened! So that was one of the first things I did after siting the shed and an access path!
They are definitely a timely process, but as you have said, if you don't mind "Getting down n Dirty" All the very best of luck with it! 
I now love to finish work, go down there n potter! I Love it!