VISA for Malawi, Mozambique, Botswana and S.Africa (Lusaka)

People,

Maybe someone was traveling to Malawi, Mozambique, Botswana and S.Africa from Zambia? Iam looking for info on the requirements, in regards to VISA? Can you just buy VISA on the border, as it is in Zambia, Tanzania, Kenya and other countries. Or you need to book it in advance?
Any other specific requirements for these countries?

Regards for any info,
Bernardas