Driving LED strip from microcontroller
For 1.5 A at 12 Volts, switched by 3.3 Volts, here is a MOSFET solution that would work well. The MOSFET suggested here is an IRLML2502 available from eBay and other sites for as little as $2.35 for 10 with free shipping.







simulate this circuit &ndash; Schematic created using CircuitLab

The IRLML2502 has a maximum on-resistance of 0.08 Ohms at 2.5 Volts gate voltage, and less as the gate voltage gets closer to 3.3 Volts. It can withstand 20 Volts Drain to Source, so it will work well with a 12 Volt supply. Drain-Source current rating is greater than 3 Amperes, providing over 100% margin of safety.

At 0.08 Ohms and 1.5 Amperes, the MOSFET will dissipate 180 milliWatt when fully on. Even allowing for the switching edges of the PWM, dissipation will not exceed 250 mW or so, hence no heat sink is required for this application. 

Regarding the assumptions:


NPN transistor drop and dissipation are correct, give or take a bit due to Vce of specific transistors
Chunky transistor (BJT), not really, but a TO-220 size would be typical, and yes, a heat sink would be required
Yes, see suggested MOSFET above
Not correct, there are several low-cost MOSFETs that turn on solidly well below 3.3 Volts, and can easily pass 1.5 Amperes
No, with an NPN BJT there is always a balancing act around base current etc. MOSFETs being voltage driven devices, work with less fuss


Some of your assumptions are correct. This answer provides one better way, and I am sure there are others.