Stuart, besides the basic equipment, you will need end mills, lathe tools, drills, taps, dies, gas torch for silver soldering, possibly needle files, nice sharp files for brass, possibly a gauge and pump for home water boiler hydraulic testing, stuff for painting etc etc, the list goes on. Add to that list, chunks of metal, tubes, fittings, nuts and bolts, rivets etc. Don't be surprised if that lot adds up to more than the price of a lathe or mill.
I have just about completed a SPEEDY 5" loco using a Boxford and Warco Major mill. I had to replace the milling vice with an ARC Euro one (I like it) and purchase a low cost rotary table. Although I am retired, its taken me about 10 years to complete – there always seems something else that takes priority !
Bob