I think he would clean up/shape up/trim up fine for a recreational trail horse as a gelding-- but I agree wit the others-- NOT stallion material at all. He really does not look typical of a good working Quarter Horse-- too lightly muscled, coarse head, thick "upside down" neck that ties in really low on his chest, and he just doesn't exude QH "breed quality" like a stallion should.
Here is a perlino AQHA stallion for sale-- While not "perfect" in conformation, he is alot closer to the QH breed ideal, and he is also a proven perfromer and sire.
DreamHorse.com Horse ID: 1626342 - RFF Starbuck
To answer your question about what colors a cremello will sire-- Since a cremello has 2 copies of the cream gene, they will always pass on a cream gene. The rest will depend on 'what else' they are genetically, and also what the dam contributes-- common possibilities for offspring include palomino, buckskin, and smokey black, but again, that is depending on the additional genetics of both sire and dam.
Here is a great website with a color chart and photos of the various dilute colors-- enjoy!
CPEA Color Chart