What is the difference in meaning/connotation between the two words? Is endorse "stronger", more positive?
Also, endorse is to endorsement as condone is to what? Is there a noun counterpart?
To "endorse" is to say that you approve of something, you are for it. To "condone" is to say that you accept or tolerate it. You condone something that you think is a bad idea or a wrong action but that is forgivable or understandable given the circumstances. You endore seomthing that you think is a positive good and that you encourage. So yes, "endorse" is a much stronger positive.
thefreedictionary.com lists "condonation" as the noun form of "condone", but I don't recall ever seeing this word used. If you need it, it's there, but I'd avoid it as unlikely to be familiar to your audience.
Endorse has a more positive connotation than does condone.
Condone means you have overlooked an offense (possibly without comment). It is often used in a negative sense: "I cannot condone your behavior."
Endorse means you give something or someone a thumbs-up, an approval, and your support, usually publicly. There are numerous examples of its use in this American election year.
The noun form of condone is condonation, defined as: the act of condoning, especially the implied forgiveness of an offense by ignoring it.
They mean completely different things. Merriam-Webster has
ODO has condonation for the noun.