What to do with my new veg patch

How lucky are you - getting a veg garden and greenhouse complete with a vine
Think you need to think about picking the toms and bringing them in, for the green ones to ripen indoors, by the end of this warm spell anyway.
First thing I would do is give the plot a digging. This way you will get a feel for what sort of soil you have got and expose any pests in the soil for the birds If you have inherited any garden compost I would dig that in as well.
I'm a bit wary of buying in manure at the moment because of Aminopyralid problems (use the search button if you don't know about this) and would prefer to use chicken manure pellets, or fish blood and bone, and I add these in the spring a few weeks before sowing.
Lots of other ideas to come...........

 The first thing I would do AledE before all the good advice above is to sit down with a pencil and paper and map out what you want to grow/how much/ and where. Then you know where to manure (not root crops)and where to leave alone.

"Do I dig in some manure/compost now, or wait until spring, just before sowing?"

My recommendation is that you divide your plot up into 3, 4 or even 5 [depending on how big it is] equal-ish sized areas and allocate each "zone" a crop so that you can rotate the crops. See:

http://www.allotment-garden.org/vegetable/crop-rotation/index.php

Once you've done that it will define which areas of the plot need manure (you don't put it on the area for Carrots and parsnips, because it tends to make the roots fork).

I would recommend this book as a useful guide to what to plant when, and how to look after it. 

Dr D.G. Hessayon The Vegetable & Herb Expert

Its more of a reference book than a detailed "How to grow Veg". For a more descriptive book, covering digging, feeding, and all the other aspects of growing veg, have a look at John's books:

http://www.allotment-garden.org/book/index.php

order from this site and he'll send you a signed copy (and some seeds I think?)