Well I'll enter this mine field ! Speaking as home shop guy with 40+ years of experience you need as a minimum a 12X36" lathe with a couple of exceptions I will get to later. You need a spindle bore of at least 1-3/8ths ,a quick change gear box ,steady and follow rests,3 and 4 jaw chucks,live and dead centers,QC tool post,drill chuck for tail stock, and a lot of misc tools to suite the work being done.
As to machines depending on tooling with machine as a minimum $2000 with no tooling ,$4000 for one with at least most of what I listed above.And remember old out of production machines will be hard to find and $$ if you do find accessories for.
In used American made machines the South Bend Heavy 10 or 13" ,or Logan 11-12" machines and rarer Clausing 5913 or 5914. Then we get into machines frowned on around here, the mostly Chinese imports in the home shop grade which as far as being usable not all that different than what i listed above.Again these also will be hard to source parts-accs for.
Power requirements -most all of the SBs and most of the Logans and Clausing's will be 220-240 3 phase which is not a big thing to deal with. The imports due to the market they were made for will be 220 with some that can be changed to 120.
Nice to have area ,I prefer gear head lathe with vari speed second with belt change a far third. A taper attachment is nice to have but not a requirement for your work but they $500 or more to lathe value and trying to retro fit one will be $$ and or hard.Spindle type cam lock or L long taper preferred over threaded.
I have owned all 3 of the American brands I mentioned in the 10-12 size range, also the imports from 10' to 18" swing . The biggest issue with the imports is the quailty spec'ed by the importer ,some identical looking machines will be of very different quailty .I have seen this in some of the Chinese lathes that I have owned or worked on.
Your location will have a big bearing on price and availability. I have a 5914 Clausing with hardened bed, taper attachment,4 chucks ,follow rest,hand wheel 5-C collet closer,Swiss Multi Fix tool post,drill chuck etc. With a 2HP rotary converter system that I'm thinking about selling . Figure about $3750 pick up in Phoenix.This is a vari speed 3 phase lathe. As I'm over 75 I'm starting to down size a bit.
Hope this long winded reply gives you a idea of what you need to look for.Good luck and happy chip making.