I would recomend getting a wormery that has multi layers, such as the
'can o worms', this would make harvesting finnished compost alot
easier, as in a dustbin style wormery, you have to dig out the top
section of rotten stuff, to get to the soggy compost at the bottom,
also the worms should have more of a surface area to do there work,
and more air.
I have a few wormeries, one of which is just a regular 250 litre
large black composting bin, i blocked off the bottom with a plastic
bag, and put some twigs ontop of that, then a perforated plastic bag
onto of that, the effluent now collects on the bottom layer, and keeps
the compost from getting water logged. this bin has become filled in a
year with food waste and grass cuttings. So i would sugest a can o'
worms for easy use, and a very large composter for garden waste, the
composter has been a excellent breeding ground for worms, as there are
stacks of them. large composter cost about £15, and a can o worms
costs £60 ish, but there are cheaper ones of a similar design.