What are the chances of a promoter signing an heavyweight amateur that only has 10 fights ?

Little to none. It really doesn't matter how many fights. The question should be who does he know and who knows him? Does he have a manager and, if so, who does his manager know and who respects the judgement of that manager.

 

He would need sometime of gimmick that would make him marketable.
Like being the first transgendered HW or something

 

Is he 6'08" with an 85" reach?
or an out of shape Cruiser-weight?

 

Depends on the fighter. If there is enough hype behind him and he’s sought after people will sign him. But most fighters don’t need a promoter to turn pro. They need to sell tickets on a small show. Do that 10/15 times against journeyman and someone will pick him up. Dillian Whyte turned pro after 7 amateur fights. One of those was a win against Joshua which then gave him a perfect sales pitch for the rematch in the pros.
He did very well in that fight and Matchroom signed him

 

That will work if the goal is to eventually cash-out small-time. More important than the amateur record, is the Heavyweight Height-Reach? Is he as big as the top 3 Heavyweights today?

A young Heavyweight with no Olympic Gold medal should be at least 6'08" & 85" reach, otherwise he needs to be at maximum reach/height at the lower divisions. Future small frame Heavyweights will have to be exceptionally skilled, even more than Holy-Tyson-Usyk, unless they just want to make a living of becoming popular Heavyweight opponents for prospects.

 

Go to Tijuana , get a couple pro wins under you then comeback with a nice padded record!