Ernesto, with the M8 you don't need to switch to anything (although you might want to take in B&W so you can preview but it is not necessary).
Yes you need a filter, and preferably a proper IR one that costs more than 50 pounds for a decent result
I usuall shooty at 5.6 or 4.0 and run through a progressive focus series.
Nick, Does this means that the M8 is sees infrared light anytime?
Even when you take normal pitures?
Ernesto