One Night In Havana
 

Need to get home from Grand Cayman to LA in business during next winter.
Prices are insane; but GCM-HAV, 25 hour overnight, HAV-MEX-LAX is quite reasonable.
Was thinking I'd stay at local-ish hotel https://www.hotelcandil.com/.

Is there anything I'm not considering as an American traveling to Cuba?

My thinking is GCM-HAV-MEX avoids most US scrutiny.
And I'd keep some museum receipts (and argue hotel is casa particular?) if ever asked to retro prove it was a "Support for the Cuban People" trip.

$25 tourist card would buy at GCM airport check-in.

Your thinking is a little flawed.
You do not need to "avoid most US scrutiny". US passport holders are free to travel to Cuba and nowadays it is easy, requiring only a passport, US OFAC declaration, Cuban tourist card and health insurance valid in Cuba. The green tourist card should cost about $20-25.
You might get a better idea of the culture by staying with a Cuban family, instead of a hotel, or in an apartment run by a Cuban family. Many hotels are not good value for money, very expensive and not more comfortable than a casa.
On return to the US, most travelers are simply being greeted with a Welcome Home, and nothing more in the way of scrutiny. You may be asked how much rum or how many cigars you have brought in though.
Many travelers departing from the US are using the OFAC reason for travel "Support for the Cuban People", which implies spending money with independent CUban businesses like casas particulares. However, museums belong to the government and do not fall under that category. Receipts are very rare in Cuban culture.
Just go, don't overthink the situation, and have fun.

^ Might not be so easy anymore, given recent announcements on travel restrictions. Those who bought their airfare before the 5th of this month are exempt from what I understand though.

Not a link on the topic of the bans, but might be helpful to those eyeing Cuba in the future.