Arriving from Tanzania, no yellow fever certificate is required: WHO does not list Tanzania as a transmission risk. It can still be demanded if you have been in a risk country shortly before arriving.
Other entry requirements
Passport validity — The UK Foreign Office says your passport must have an expiry date at least 6 months after the date you arrive in Cuba and 3 months after your planned departure date.
D'Viajeros traveler information form — Cuba's D'Viajeros site says it is mandatory for each passenger to complete the advance traveller information, truthfully, for the Immigration and Foreigners Directorate, the General Customs of the Republic and the Ministry of Public Health. The UK government says to complete it within 72 hours before entering Cuba, that you'll get a QR code by email to show on arrival, electronically or printed, and that airlines check completion of the form at check-in.
No official source states a rule on: proof of funds.
International Health Regulations (2005), Article 36 and Annex 7; WHO International Travel and Health, Annex 1, 18 November 2022 (revised 3 January 2023)