There are no direct flights to Yemen. It is generally mild inland with cool nights, but can be cold in the highlands in winter. Coastal areas are hot and humid, prohibitively so in summer. Check the dates of Ramadan. There are few bus services and it can be difficult to get clearance to travel independently from tourism security.
Organised tours are best.
Vaccinations aren't compulsory to get into Yemen, but check with a travel doctor. Mariana Hardwick takes specialised tours and organises independent trips. Tours takes eight-day tours or will tailor one. Phone 1300 362844.