Like you, I have one large quilt now in four sections and basted together and ready to quilt on my DSM. Right now it is at a stand still so I have a good Idea where you are. I guess I am going to put it to a frame and hand quilt it to get out the bicycle clips and roll each section as best as I can. When all that is done I will put all 4 pieces together with a thin border or QAYG to bring the quilted pieces together. Right now this wonder is sitting aside. This may be the year for UFO's and if that is the case then this one will be at the top of the list.
I hope you get a lot of good ideas so you can get moving on this wonderful quilt. I have no real ideas on how much to leave on the overhang to complete your quilt. Best of luck.