My 3 adults have a shallow stainless steel dog dish ( so they can all share nicely
and it's easy to clean )
I give them 4-5 veg choices twice a day so about a bowlfull.
YY to keeping an eye on their pooh and weight (pooh not si easy if there are 4 bottoms but we find ours do pooh nests so we can keep track)
If I give a carrot with leaves, a half pepper, 2" peice of chicory, handful of kale and some herbs, then it gives them variety and there will be something they all like
Then maybe for supper they'll have different herbs, half a red topped baby lettuce, handful of spinach/watercress and rocket salad and a sweetcorn cobette.
They have loads of hay and two scoops pf pellets.
99% of the time everything is gone unless it;s cauli leaves or turnip peel that I put in to trick them into the bowl being full.
Kale is eaten last as protest "to keep us regular" they sigh.
If they have grass then I give them less veg/more hay
Although it is hard to overfeed them, I do wonder how they get so lardy on veg 
I did read somewhere that they are meant to have their veg at night but mine would be up all night whittering when I want them to quietly pooh eat and sleep.