Below are pics of my panama berry (Muntingia). I have planted it into my lawn which has about 10-15cm of decent topsoil, under which is quite heavy clay.
At the moment, I have left a patch of bare ground in a 15cm radius around the tree with no mulch. After that, it's just lawn grass.
Would it be a good idea to enlarge the circle and put down some sugarcane or wood chip mulch? Would it be a good idea to use some bricks to make a border around the tree to make it easier to exclude grass from encroaching?
Yes I'd definitely mulch out a bit, both to help hold moisture in the soil underneath, and to prevent the grass from growing in as competition. You could also plant ground cover or shrubs around the tree to make a guild, Edible Acres just put out a video reviewing several they have and explain it nicely in this video:
I'm not quite a lumberjack, but that's OK, I sleep all night and I dream all day; I'll coppice trees, I'll grow my food, and compost poo and pee! With a well and off-grid solar, it's a permies life for me! https://www.youtube.com/watch?v=FshU58nI0Ts