I do lots of tee shirts and they turn out lovely every time. I use the hoopless method (spray lightly with 505 and position tee) with a polymesh stabilizer, never a tear-away. Unless the tee shirt has a nap there is no need for a wss. I do pin around the edges of the design well out of the stitching area. I use a template to position my design and make a mark with water soluble pen to mark the center. Using a tear away stabilizer can lead to stretching and possible distortion of your design. The polymesh is soft but very strong and much more comfortable for the wearer. Just trim it carefully around the design.

wws would go on top of you fabric. If you are using scraps of wws you will need to pin or fasten in some manner so it stays in place. If you use a large piece you can hoop it all together. I haven't used sprays much. But I think the idea is to hold the fabric and stabilizer together so they don't shift during embroidery.

I use a product called "Cover Back" on the inside (especially for children) and also use cut-a-way that is adhered to the t-shirt and hoop all together unless it is a tiny one then I use the method mumra does. I do always use WSS (water soluable stabilizer)on top it seemed my needle was punching fabric down until I started doing this. ;)

I like the poly mess backing on shirts, and this does not show through on the design. Too, sometimes the desing makes the shirt itchy, and this also prevents that. I do not hoop most of my projects. You have been given very wise considerations.