I have made several. While the .99 cent Jo-Ann fusible is functional I prefer the slightly heavier, better made Pellon brand name fusible. Lightweight for knits. It may cost a bit more but it is definitely a sturdier product and you don't have to concern yourself about which way to lay it and iron on so that the fusible stretch is going the opposite direction of the T-shirt knit stretch.
I have used plain quilting cotton for sashing and I have used no sashing and simply sewed interface T-shirt blocks together. Until I got my LA I tied T-shirt quilts. They are incredibly heavy and really difficult to attempt to quilt on a domestic machine so unless you plan on sending it out or have access to a LA I would recommend tying it every 3" to 4". When I tied, I went right through the imprints and used 3 strands of embroidery floss. Another thing, carefully examine your imprints. The rubbery Iron on kind aren't suitable. And ALWAYS use a pressing cloth. The heat from your iron will melt the ink used to screenprint the T's if you don't.
Here is alink to a pic of one I tied
http://www.quiltingboard.com/picture...lt-t47094.html
And here is a link to one I LA for a friend:
http://www.quiltingboard.com/picture...ts-t95274.html
When LA I went right through imprints. I only avoided heavy machine embroidery.