Pots -- as big as possible, &
reuse where possible are my main criteria personally
I have long been torn between ceramic (look nice, more
sustainable, can use the pieces once they break), and plastic (hold water far, far better, lighter which can be important if on a roof/balcony). But I'm honestly not very picky about pots -- if it holds earth and drains, it's probably good
though of course different plants need different depths/sizes.
You can absolutely grow trees in pots, although you need a pretty big pot for the tree to do well. A dwarfing rootstock is generally a good idea, probably self-fertile unless you have lots of space and want to grow lots of trees, and as with all container gardening, it will need more feeding and watering than a tree in the ground. I currently have a cherry in a pot but it's only 2 yrs old so not fruiting yet. Fig trees do better with their
roots contained so could work well. I did try a satsuma tree but it never fruited -- possibly I bought the wrong cultivar and it wasn't self-fertile, possibly it never got hot
enough for long enough, possibly something else. I live near Downings Road Moorings on the Thames, a collection of barges which have beautiful floating gardens all of which are effectively container-grown (though very big containers -- some of them are basically the whole top of the barge filled with earth -- more info here
http://elainehughes.co.uk/?page_id=647 )
The plant in the photo is Swiss chard! It is in the process of going to seed -- they get absolutely enormous (5-6 feet sometimes) and then you have a vast quantity of seed. Unfortunately to breed true you have to remember to tie the tops in a bag at the crucial point, as they're wind-pollinated and will cross with any kind of leaf beet thing within half a mile. I am very bad at remembering to do this (and even worse at remembering to cut them back before the seed goes everywhere) so my 2nd generation seed tends to be an excitingly random selection of green leafy things with variously-coloured stems, popping up at random across the garden
it all tastes OK though...