Welcome to H-M.
Turkey is a beautiful country. I've been to both Istanbul and Ankara. I have not been as far east as Kayseri. Istanbul is one of my favor places.
As for bearings, I believe you would want Annular Contact Bearings or Tapered Roller Bearings.
This page introduces News releases. What Are the Differences Between Bearings? The various types and special features of bearings
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Whether Annular Contact or Tapered Roller Bearings, each bearing should be installed "opposite" the other, (back to back), so they can be preloaded to take up any end play.
Depending on the material you expect to cut, Aluminum, Steel, Brass, etc and the loads, you could make the headstock from Aluminum.
Sherline makes a lathe similar to the dimensions you are looking at. Their Headstock is made from Aluminum.
Here an exploded view for your reference.
As for Motor Speed, again it depends on the material you intend to cut. Materials such as Aluminum cut has higher speeds than Steel. Having speed ranges from 250 RPM to 5000 RPM would work. As the diameter of your work piece gets smaller, you'll ideally need higher RPM to keep the SFM (Surface Speed) up.
Hope this helps.