Ok - i know you have to choose the equipment (lathe/mill/lefthanded sproggle whatsit) according to what you want to make.
But how are you supposed to know that until you have started?
Take my woodwork lathe. I thought carefully about the first and chose one that would do long posts and big bowls. And upgraded it two years later becuase it wasn't precise enough and i didn't want to faff around changing belts to get the speed right. and i still haven't done a huge bowl or felt the slightest inclination to make a fourposter bed with cherubs carved around the top. But i did taper a catamaran mast for the youngest son which was longish - and made a large disc sander attachment for flattening which is wide-ish.
So what do i want for metalwork? I did try the "buy what you need when you need it" approach for woodcarving gouges, router bits, er, etc- but that doesn't work either becuase you have started the job. I can't plan far enough ahead to realise I'll need a 6mm ball bit for getting rid of 20 seasons of varnish in the bolt rope groove of my boom so i try and manage with what i have. (Ground an old cabinet scraper to a ball shape and used paintstripper)
So i don't actually know what i want to do. I do rather like model rains - but i can admire a 3.5inch model of a bulleid pacific without feeling much inclination to negotiate with the council to run track around the house or spend the next 5 years making one. Static steam engines and traction engines don't fire my boiler. I quite fancy making some more model sailing boats - but not the sort with tapered brass cannon barrels. The eldest kid has been a robotic wars fan for 50% of his life. I read a book about making jigs and tools for your workshop so that you can do certain jobs better but I didn't notice him making anything I actually wanted.
So, I'll try it another way - what is on your workbench?
Recommnded reading lists for pre beginners are also most appreciate.