There are some different types of swithes.
1) magnethic switches.
When you are intent to cut ferro materials it can be happen
that your material is light magnetic and can produce a false connection.
So, i prefer not to use magnetic switches.
Every type of dust, especialy when you engrave wood, can
activate the switch and your program will be stopped.
You can also have problems with coolant.
So, i prefer not to use optical switches.
When you protect the switch from cut off material you have the
best solution for referents.
The most of the professional engraving and milling machine are
using mechanical switches.
How many switches.
when you are using 2 switches, you can connect them parallel to 1 port.
(see figure 1 and 2 )