Mesa Card Basics

It'd be ok for driving the steppers and some extra outputs and 5 inputs. Really depends on how inputs you need.

That's the common "Mach 5 axis" breakout board (BOB)
that's compatible with 7I92t_5abob.bin firmware.
It does have 5 inputs

 

quite new to mesa and llinuxcnc myself, few doubts retrofitting an older machine
all 3 axis + spindle are all AC servos that use resolvers for feedback, does this mean I can use 7i49? and can I use its 10v analog to control the motors respective drives?
moreover, I've seen it elsewhere paired with 6i24 fpga, but online ive seen variants of that with 16, 24 and 50 pins, how does this affect my usage? are these related to I/O pins?

If the resolvers go to the drives(and this would be expected for AC servos),
the drives themselves have the resolver interface, so a 7I49 is not needed.
What hardware is needed to interface to the drives themselves depends
on what interface modes the drives themselves support.