Having not seen the lathes that you are interested in, what about using the head and tailstock from the inexpensive lathe and fabricating a new longer bed. I have seen inexpensive store bought lathes that use angle iron for a bed.
When using a stepper motor, use a toothed belt to drive it. Using a v-belt on a stepper is not a good idea. As for spindle tapers, go with the MT#2. There seems to be more available tooling out there to fit. If you need to go smaller for a tool you can always get an adapter.
If it's not nailed down, it's mine.
If I can pry it loose, it's not nailed down.