The best and safest way to cross from Malawi to Tete is to take a bus from Blantyre to Harare (maybe “Flying Horses” from the Central Bus Station) – you have to pay for the whole trip, but it will be a comfortable one, and the bus stops in Tete, where you can disembark!
Ideally, get your Mozambican visa in Lilongwe, as it’s much easier than to buy it on the border. On the border, it can be that they want to see your Yellow Fever Vaccination! Don’t forget it!
In Tete you will find several options (TCO, LTM) for buses to Chimoio, Beira etc