Lathe motor mounting

That's a pretty standard mount, but I'd add a bungee cord or two to slow the motor's "climb" on startup. I like the cheap black rubber type, as it's not as bouncy as the circular types. Opposite the pulley end helps balance.

The motor, once aligned, will stay aligned. What you do is take advantage of the built-in adjustment available in the motor mount, or build some into your plywood by making the bolt holes longer.

As far as speed changes - I'm not your guy. I cut everything at my low speed of ~500.

If you will be switching belts in a non-symmetric fashion, a "hinge" with some sideways "slop" will help the motor line itself up. All the quotation marks are because I've never seen a hinge as such that has enough slop to make this work, but I do have a motor or two mounted to pivot on a shaft with some sleeve bearings that act as this sloppy (sideways - quite well-fitted rotationally) hinge. If you will always be stepping up on one pulley and down of the other, getting it lined up once when mounting should suffice.

A spring or something to help keep the motor down is good, as is a means to slack it off when stopped (can also put in a pedal to allow slacking it off as a clutch mechanism when you would like the lathe to slip a bit easier).