Well, you should be fine with darlingtons because of their high gain, but keep in mind that BJTs do draw significantly more base current than MOSFETs draw gate current.
If you have high current demands on the darlington outputs (like, lots of LEDs in parallel on one transistor), then if the hfe of the transistor is low, you might draw some base current. driving lots of these bases could exceed the total current output limits of your arduino. however I think youll be fine. especially with the current-limiting resistor on the base - that way if it starts to draw lots of current into the base, the voltage at the base will be lower and start to turn the transistor off.