For what it is worth, my twopence worth.
What is the intended printed format. As a work of art, to be displayed? or maybe incorporated into something like a printed poster, t-shirt, mug or ...
Do you have a home set up where you can reliably guarantee what is displayed is the same as printed? That means a good quality colour calibrated monitor as a start + a good bit of knowledge. However, probably 99.9% of your customers will have nothing like that, and will see something different from what is intended.
Include a disclaimer with your work. Be prepared for whiners.
Do you expect potential customers to print at home or send the designs off to a commercial printer? If the latter, then the requirements depend on the printing company.
Good quality printed artwork these days will probably accept RGB images. One local artist I know, quite expensive, inkjet printed on art paper with archival quality inks. Definitely not home printing.
Posters are more likely to be CMYK - pulled this out of my references,
http://www.northlight-images.co.uk/cmyk-...jet-print/ A bit technical but worth a skim through.
When it comes to CMYK versus RBG, Gimp is purely RGB. There is an old plugin
separate+ that will export a CMYK image and import one as well, but any editing will be RGB. There is a colour shift between the same image in RGB and CMYK and varies with the CMYK .icc color profile used.
Need images in CMYK? Do not use Gimp, use Krita (free)
https://krita.org/en/ where you can start and finish in that mode. Krita will also convert between colour spaces.
best of luck.