I need some t-shirts designed and a label created

I need someone to help me create t-shirt designs and a very simple logo, featuring my original artwork. I would like to use the website inkthreadable.co.uk so the designs need to be to their specifications and I would like the freelancer to create the designs and then put them onto products (t-shirts) using the website and my specifications about brand etc.

I would like to start with 5 designs and they should be fairly simple, featuring the art quite clearly and centrally, but I am definitely open to suggestions about colour of the shirt, and sizing of the image. I am sure this would be incredibly simple for anyone with even a basic knowledge of some design programmes, which I don't have!