IMHO, you should interface the t-shirts before you start cutting them. Otherwise, the edges will stretch, curl and start to unravel. I use the Pellon Shir-Tailor interfacing for my t-shirt quilts. It feels stiff when you cut it, but once it is fused to the t-shirt, it is much softer. The cuddle factor will depend on what type of batting you use. Wool is always good. The Crooked Nickel website also has a fusible grid for 10" squares plus 2" sashing that helps make quilts like this much easier to put together. There's a video tutorial on the website.
One way to much the quilt more interesting is to use pockets, sleeve plackets, etc. in your blocks.