I hate to be the bearer of bad news, but even if the designs were good, they can't be silk screened.
All designs except your logo have heavy shading. This means they will require Simulated Process or Full-Color Separation. This is a VERY difficult thing to do and requires the best in the business to pull off, which is why it's rarely seen. The process will cost you to lose a ton of detail, and it's also insanely expensive to manufacture.
You also have too many colors. Using that many colors will cost you about $15 a shirt to screen, plus the setup cost of creating a screen for each color. Try to keep it down to 2-3 colors to keep the shirts cost effective.
The only way you can really pull this off is to use a technique called Digital Print, which is absolute garbage. Put it through the washer and dryer twice and the shirt is ruined.
Again, I hate to be the bearer of bad news, but I figure it's best to find out now rather than later.
Sorry man.
EDIT: Here, read this for a quick summary:
http://ezinearticles.com/?The-Pros-and-Cons-of-T-Shirt-Printing&id=2151396
EDIT #2: I just noticed that you're using an 'on demand' printing service. They'll use Digital Print for sure, which... well....at $28 per shirt, you're going to have the worlds angriest customers (shirts made with Digital Print usually retail for about $12-$15 because of the low quality).