Based on his presidency, he'd clearly be an advocate of the use of soft power, not hard power. To the extent he would get involved in the Russian aggression against Ukraine, he'd limit our reaction to sanctions and embargoes.
As for Sally Hemings, it's doubtful he'd have married her and far likelier he'd have gotten caught up in the #MeToo wave.
if Jefferson were alive today and in a relationship with Sally Hemings, I don't see why he wouldn't marry her. firstly, virtually no one has any problems with interracial marriage now, and secondly, she wasn't even black - she was mixed.
If he'd wanted a wife, Jefferson could have easily gotten one. Jefferson wanted a concubine, not a wife; he got what he wanted.