If a man has the din of חייב מיתה and performs קידושין, is his קידושין valid? We know that in the case of a man whose חייב מיתה, if a person were to go and kill that man, the man who killed him would NOT get מיתה בידי בית דין.
(Disregarding your claim that
The Mishna in Arochin (1:3) says:
See that Bartenura there that all agree that he can be ומקדיש- as in "make it Holy".
The argument is whether he pays for items he damages.
There's no reason to assume he cannot marry somebody; the Rambam would have codified it somewhere...