Based on the choice of what you want to grow I guess you will be available fulltime to manage the farm operations or have someone to do it.

As you hunt for a potential buyer watch out for conmen who are basically out to sell farm inputs with promises of how they will market your products abroad.
I.e whatever you can get from a kawaida agrovet will be sold to you at double the price with stories of how they have selected the inputs meeting their standards.
While addressing the issues for your preffered crops you could try growing kawa stuff like sukumawiki, beans etc to raise a few hundreds rather than the land stay idle.

Agribusiness is a full time venture, never understood those who think they can farm through phone calls and MPESA. Harvesting time is a killer, if you are not there utagongwa. Have you though about integrated crop and livestock farming?
My advice is: look for the markets first before planting anything, identify if it's worth it and surround yourself with experts/farmers who are involved in what you are interested in planting.