So the only thing i should be careful with is not to input into an(d, edited)
output pin ?
It you tie a voltage to an output pin, you can get a damaging current. The simplest
way to protect an output pin is to tie a small value R in "series" with it, eg 150-330
ohms, then if you accidentally connect a voltage to the pin [which happens all the
time], you won't damage it.