Hi Dan - not sure where abouts you are or what your land & other environmental factors are like ...
You'd be surprised how much you can get into a 6x6m area - especially as there are so many nurseries grafting heavy cropping varieties onto dwarf rootstock.
Have a look on various fruit tree grower websites, so you can get an idea of the ranges available, how long they take to produce a crop, what will be suitable for your land and space (and the costs!). Go for varieties that you like and will make use of. Remember to check if they are "self-fertile" or need a cross-pollinator.
We've got a range - Medlar, pear, quince, eating & cooking apples, cherry, plums, damsons and crab apples in our small orchard area. With hazel, blackthorn (sloes), hawthorn, Rowan and Elderberry, with more crab apples & damsons in the hedge-line weaved with hedging and wild roses (for the hips). You can make use of "under-planting" - we grow gooseberries, blackcurrants, jostaberries, wineberries, in between our orchard trees too, with a line of raspberries dividing one side of our orchard from our vegetable area with loganberries and tayberries growing up a boundary fence.
As long as you prepare the planting-hole well with the nutrients the trees need and keep grass away from the trunk by at least 2ft, watering well the first growing year there isn't a huge amount of maintenance needed - occasional feeding and watering when it gets really dry, some varieties need hardly any trimming at all.
Also a good idea to keep bees to help with the pollination too