In syntropic agriculture they say that one man can usually take care of about one hectare which is 2.4 acres using syntropic methods which can be a little bit more labor intensive. And that's if you're working on it full time. But that's also an average if you're a hard worker I think you could handle a lot more than that I have been maintaining approximately one hectare but I don't work everyday. I probably work one day of 10. I'm working in a tropical environment which I think in the long run is less work because you have increased stratification more shade tolerant plants and it can really become a stable system. Of course initially in a warm environment with lots of moisture it will be difficult to maintain things. My advice would be to start on a small area and once those plants are well established and they can handle a little bit of neglect then move on to establishing more areas. If you're in a temperate area I would definitely recommend raspberries is one of your understory crops and some species of Dioscorea depending on your latitude. Another really great plant for maintaining the understory of an orchard is the Canna edulus these plants can take crazy amounts of shade and they can produce a carbohydrate rich tuber. Another plant that can take a lot of shade is capsicum pubescence but it is a long season crop and does not take Frost. Basically the more shade tolerant crops you have the easier it will be to maintain if you're trying to maintain the orchard while letting in crazy amounts of light then weeds will be harder to maintain. The best thing to do is to fill up those areas, block that light and also create competition for nutrients.