Martin, I use a Boley 8mm watchmaker's lathe for most of my repair work, and more recently, a Unimat SL for which I'm sorting out more accessories, I turn brass and steel in equal measures on these machines – admittedly not big cuts or big hunks of metal – unless you include clock winding barrels!!
You won't be able to carve chunks of metal as you would a bigger lathe, so things will take a little longer and need a bit more patience when carving off a lot of waste!
Both these machines are smaller than the Unimat 3 and I get by just fine, it all depends what you want to do with your lathe, but to use either lathe I sit down, I have to due to a spinal injury which prevents me from standing for long periods – and why my Myford gets so little use!
I use an armless swivelling office chair of the type with a hydraulic lever set height adjustment, it works a treat and is more versatile than a fixed stool, you just need to make sure your legs and the feet of the chair aren't obstructed by anything under the bench!
For the bench itself, this was constructed with the work surface higher than normal, which gives a more comfortable working height, but mine is rigged principally for clock and watch repairs and the need to get closer to the workpiece – on occasions with a binoccular microscope!
You'll work out an average bench height to suit you eventually, but try to avoid having your head down too much, otherwise you may suffer suffer neck related pain and headaches! (hence the higher bench, because with the seat height set too low, your legs will get cramped)!
Sitting down at a lathe admittedly isn't the ideal position, but some of us have little option and necessity is the mother of invention, fortunately nothing that has flown off either lathe has clipped me yet, or maybe I'm still able to move a bit quicker than stray bits just yet!
John