Screen printing is not like other processes. You don't just hit print and out comes a shirts. The time/cost comes in making, aligning, and cleaning up each screen. If you are printing a small run of 24 shirts, each additional color or location compounds that time. The screen time is actually longer than the printing time. On a larger run of 150+ plus shirts the screen setup time is less then the print time, so the cost per shirt goes down. I'll post a video that shows the whole process.
This is a little complicated. Please see the FAQ about Photo size that talks about how large your photo should be. Logos are best as vector format (Illustrator or some PDF file formats). Meaning they can be printed large and still crystal clear, vs. jpg's that can look blurry if you print at a larger size. Please try to send the largest jpg that you have to ensure the best print quality.
Photo size is based on how big you are printing it. The recommended size is 300 DPI (dots per inch or PPI pixels per inch). So if a photos is 5 inches wide at final print size in your layout...it would be 5 X 300 = 1500 pixels wide. For large format the viewing distance is usually greater than 4 feet, so the photo should be 72 DPI at final size. So if the photo is 24 inches wide it would need to be 24 X 72 = 1728 pixels wide. There is some flexibility and tricks if your photo is smaller, but this is the recommend lowest sizes.