I have the feeling that the Chinese already have a perfect plan. If I were a dictator I would import a few Chinese families on the farm, start working. Then hire a group of Zanu-PF thugs to cause trouble since the Chinese somehow tick Mugabe off. Mugabe arrests said Chinese, then the Chinese have the perfect excuse to off Mugabe and seize control of the country.
Mugabe needs help propping up his dictatorship. He needs people who can actually operate a civilization.
Continue buying land, and paying for it with manufactored goods. Import young Chinese men of military age to operate the farms. Avoid conflict until you have a million men in Zimbabwe. Get "self-defense" arms smuggled in for the Chinese farm workers. The ZANU-PF thugs will not be anxious to fight the Chinese, and would be exterminated in a couple of days if they did
Then you have a million-man army right next to South Africa and the world's richest mineral supplies.
A quick thrust to take a South African port, and you have a hundred Chinese container ships offloading tanks and heavy equiptment to finish the job of conquering Africa