What kind of sensors and what do you want to do with them?
The only issue that usually befuddles Mach 3/breakout board users is the limited number of inputs. The usual answer is to use multiple home/limit switches on one input. Unless you have a double X axis (4 axis, two drives on X), you can get away with as little as one input for all home/limit switches.
There is only a switch (binary) input on the basic breakout boards. The only inputs Mach deals with natively are the home/limits. Various add ons use different inputs, some of which (like modbus) can have values other than on/off.