Welcome Rufaro's mum! It is a pleasure to welcome you to this site!
I fully understand the pressures you are under in the village, indeed you are right that change happens slowly. We will send ideas from our ecosystems but ultimately it has to work in your ecosystem, so try those ideas you find useful and do not worry too much. I understand that the margins for error are slim and ultimately you are the expert on what is going to work. You are fortunate to have such a committed daughter who learns fast and is working to cover expenses while you make the change over. I found my biggest expense as a farmer - even though my mother was a farmer and her mother before her - was making mistakes and learning from them. It is paying off now but it was touch and go at times :)
Yes, unfortunately it looks like drought this year. You will be better off with the drip irrigation and the mulch than many of your neighbours, but the outlook looks bad for the whole of southern Africa. At least the upside to this is that any maize you can bring to harvest will get good prices. Keep on doing what you are doing, no one can predict what climate change will do. The bottom line is that we are likely to have more droughts more frequently so keep on building up organic matter in the field through mulches and compost heaps. Your soil is going to have to do more with less and the only way to do that is to nurse the soil.
The pumpkin was a great idea. Other ideas for diversifying would be sunflowers (your chickens will eat them as well) and pigeon pea. You will find that as your soil organic matter increases you will be able to plant quite thickly around the edges of your field (especially where you have water run off) without affecting your main crop. In fact this will help the maize by protecting it from wind and evaporation.
Climate change is affecting Africa the worst. The research for South Africa shows that we are warming about twice as fast as the average for the planet, that is, if nothing is done we will reach 3 degrees Celsius warming by 2070. It is small farmers like us who are going to make the difference by storing more carbon in the soil. In the meantime create as much shade as you can! It is wonderful that you are planting tree in your fields, it has the advantage that as you grow your crop you nurse them well.
I wonder if you have heard of Faidherbia Albida? It is a wonder tree that draws nitrogen to the soil and loses its leaves in summer when your crops need sun. It has made all the difference in north-western Africa's arid regions and should be tried in Southern Africa's summer rainfall areas. I am about to get seed for the family farm in Namibia, and will keep you posted on developments.
The maize stem borer is increasing in Limpopo, it is a consequence of warming temperatures apparently. If it is not too late, try planting chillies in your vegetable patch. On harvest you can soak them in oil, mix the oil with water and a drop of soap, and use as a pest spray which you don't have to pay for. You may also have local plants which work, we have a form of garlic here which is much stronger than the European species, I plant it around all my vegetable beds and am never troubled with pests. We also burn impephu for the mosquitoes, perhaps there is a Zimbabwean cousin which people use? In general, any plant with strong smelling leaves will help to confuse the pests so gradually using your edges for such plantings is a win-win-win.
Best wishes for your work. Your work is building a future for your children and they will be grateful one day.