What a great quilt! I especially like the way you made half-blocks from the t-shirts and used them as the border, and used only a very thin sashing.
I can just give you words of encouragement but no advice. There area many tutorials and videos about basting a larger quilt (which is half the hassle).
Here's how some of the masters do it, regardless if you're doing a meandering stitch or dense micro-stippling. That will give you some ideas whatever method of quilting you decide on.
Sharon Schamber's basting videos (2 parts)
http://www.youtube.com/watch?v=bhwNylePFAA
http://www.youtube.com/watch?v=k_EjBGz5vGQ
Caryl Bryer Fallert - Quilting a Large Quilt
http://www.bryerpatch.com/faq/machin...largequilt.htm
Building a FMQ table (cheap)
http://www.youtube.com/watch?v=g14govA4pIM
http://www.youtube.com/watch?v=yAS25v3ZTk0