Ok... Stitching in the ditch is actually going right along side of the seam where the 2 pieces are joined. I have also heard it explained as stitching right on the seam as you asked, but I have also heard this can cut the joining threads if you have your seams pressed open.
A walking foot sort of acts like feed dogs for the top of your quilt to insure all 3 layers feed at the same speed (the backing doesn't reach the finish line before the batting and then the top).
As far as your space issue, is there any way you could stack those books and such on the floor beside the coffee table you sew on and let your quilt rest on those ? You just don't want too much of it hanging down away form your machine. Anything would work as long as your quilt can drape onto it. You will know if you need to put something there immediately because you will feel the weight pulling at the needle area as you are trying to quilt it... you'll be wresteling with it. If you have enough table top space, you can pile the majority of the quilt's weight around your machine, it will just require adjusting the quilt more often and good basting.
As for basting, safety pins placed every couple of inches work very well. If you do not have safety pins, grab a needle and some contrasting thread (different color than the quilting thread) and hand baste it the old fashioned way. Divide your quilt into quarters (mentally) and begin at the center sewing out to the edges first forming a cross then from the center out again, this time forming an X. After that, baste as many additional radiating lines as necessary to secure the sandwich together. I make stitches about every inch or so, but others may have better information about this basting method.