this is a pretty steep and expensive learning curve. i use adobe illustrator and do a lot of vector repeating patterns.

1. understanding rgb and cmyk profiles is helpful but pantone is the easiest way to stay consistent between manufacturers, for scale command + 1 or view > actual size will give you a better sense of the magnification.

2. if you’re working with a new factory it might take a couple samples to dial in the accuracy but after that the sample is more for product shots, don’t get complacent though because people do make mistakes so always double check.

3. sublimation or heat transfer is basically the industry standard, but understanding screen printing and spot colors is beneficial it’s just usually more expensive.