Other than spinning the work piece a wood lathe has little in common with a metal lathe so there is not much to learn from using one, for metal working that is. If you go with a small lathe then the 9x20, even with it's limitations, is the way to go because they are so common. There is even a couple of web sites dedicated to these machines that show how to get the most out of them, with a few cheap and easy mods they can be turned into a decent tool. Don't discount Harbor Freight if you decide to buy one of these things because even though the quality is lacking it is no more so than if the machine came from someplace else, it will just be a different color and a different price. I had access to both my $1200 Jet 9x20 and the HF version and I know for a fact that one was no better than the other, they both suffered from the same flaws and parts were interchangeable. When I bought my 14x40 lathe I bought it from HF on sale and with a 20% off coupon that let me buy it for nearly half of what Enco was asking for the same machine with their name on it and like the 9x20 it is the exact same machine.
An interesting note is that for a while the Harbor Freight 14x40 lathe had the manual/parts book for the much more costly "Brand name" Birmingham YCL1440 lathe! I have looked at the Birmingham and the only difference I can see between it and my HF lathe is the color scheme. My point is these lathes vary widely in price depending on who you buy from but they do not seem to vary in quality, my HF 14x40 has been in daily use for over three years now and is doing well. HF has little or no after sale service and since pricing has gotten closer to other suppliers I would recommend a dealer such as Grizzly or Enco.
Grizzly seems to no longer carry the 7x10 but they have the 7x12 which is the same lathe with a 2" longer bed.