motor vs spindle rpm, pulley ratio questions

 i tried searching this but was not sure if i was using the right terms.    i had started to convert a hobby lathe in the past and it worked with manual control of the spindle. had put two encoders on it so i would be able to thread etc, blew it up when i tried to control that spindle tho lol.

any ways im starting to make a lathe more from scratch.  using a atlas head stock i got from ebay. wanted a bigger thru bore and i have chucks i can use on.

i was just gonna use a vfd and a 1-2 hp motor since i have setup a few cnc routers with a vfd  and did not blow any thing up.
if my pulleys on the spindle and motor are the same size , that is easy enough to setup.
is there a reason not to run it 1 to 1? 
if i use different different size pulleys what area in the docs, link to post etc  how do i handle telling the vfd to spin the motor at the right speed to get the spindle rpm i want    i was gonna use rs485 and a huanyang vfd since i have one already. 

Thanks for the response . 
I figured I’d play around with the back gear and pulley sizes etc . Cause I figured 1-1 would be to easy lol . 

I’m just confused how I go about having LinuxCNC  handle the ratios and vfd. 

I’m smart enough to know what I don’t know.    I don’t know what terms to use to search for the info.    Like on my tormach 770,  has a button for low or hi for the spindle pulley .
I don’t know how to go about having that feature in Linuxcnc gui/ how to set the  pulley/gear ratios etc and it tells my vfd what speed to run the motor at so my spindle rpm is right . 


Or am I over thinking this , since I’ll have the two encoders for threading rpm/postion. Will linuxcnc just read that and tell the vfd what todo ?