There is a big difference between handmade and handcrafted!
I only made NPHC letters a couple of times but have made letters for NPC and IFC orgs often. If you are making them yourself, I recommend the following:
Specific Products
Dritz Fraycheck around the cut edges. Fraycheck is a thinner less gluey liquid as compared to other fray preventatives.
Ultrahold Heat and Bond for your fusing. This says you can't sew through this but you can.
General products
A clear plastic quilting ruler to center and level the letters on the garment. I use the 15" square Omnigrid.
For TShirts, I use both tearaway stabilizer AND freezer paper on the inside of the shirt. For sweatshirts, the tearaway stabilizer is sufficient.
Technique
I would definitely satinstitch around your letters as opposed to just zigzagging
