+1 for a well insulated shop.
1 ) It will be cosy and so make you more inclined to go there to work.
2 ) It will cost less to heat
3 ). And possibly more importantly, it will reduce the risk of rusting.
If you choose an older machine, it will not have the speed or possibly the rigidity to make best use of carbide tipped tools
For some jobs, you may need a special form tool, so HSS will have to be your choice.
Learning how to grind HSS tools will be useful experience for the future, anyway. Also, for the cost of one carbide tip, you can buy a length of HSS, which will suffice for MANY jobs.
Carbide tips have their uses, they will cut hardened steel that would defeat HSS, or make mincemeat of the skin on chilled cast iron.
Although using carbide for roughing and boring, I am a fan of Tangential Turning Tools. The HSS bit that came with the tool, and is my usual turning / facing tool, started life at about 1.5" long. It is now down to less than 1/2" and will soon be too short to hold. But that has taken four or five years of regular use and regrinding.In that time,
Over the same period, several carbide tips in the roughing tool, and a couple in the boring bar. have been required.
For the Tangential Turning Tool, it really needs a Centre Height Gauge, because the tool needs to be reset to centre height after every sharpening. (A simple job on just one face, with a small jig )
Making the gauge can be a good learning exercise, (Facing, Drilling Tapping, using a Die involved ) but leave a tool that will be useful for almost ever after.
It is quite likely that you will find yourself making a tool to do a particular job. As learning, Tap Wrenches, Die Holders, and then probably Tailstock Die Holders.
Toolmaking can be a hobby in itself, as can refurbishing an older machine, or improving a newer one.
And you will have the equipment to improve / repair all sorts of repair things. With the right kit, someone else's major disaster can be a minor inconvenience to you, and insurance against a future repeat failure.
You have lots of enjoyment ahead of you!
Howard