Discovered that PNP BJT's aren't good to load voltages higher than the microcontroller's supply voltage, used for the logic control wired directly into microcontroller. NPN ones are OK in this situation?
For darlington pairs the above problem of different voltage loads doesn't happen as it does for BJT's?
I was reading materials about MOSFETS and seems that bipolar transistors are good in the task of amplifying current and MOSFETS are good in the task of amplifying voltages.
Steeping down the voltage and keeping things simpler sounds really a nice idea, the only problem I see on this is that all circuit possibilities (current), are subjected to the regulator limits.
...No, they are no better. NPN bjts and N-channel logic level mosfets are good for low side switches where the low side voltage is Arduino ground. PNP bjts and P-channel logic level mosfets are good for high side switches where the high side voltage is the same as Arduino Vcc. If you want to low-side switch a voltage that is below ground (i.e. negative) or you want to high-side switch a voltage that is above Arduino Vcc, then you need to level-shift the drive to the base of the bjt or the gate of the mosfet. This level shifting is usually done by a bjt.
Bipolar transistors will need base limit resistors and a emitter-base shunt to ensure full turn off.