With the pot set to 81Ω, the LED current will be 2A. You said that you want to vary the LED current. If you do not want to vary the LED current, then replace the pot with a fixed resistor.
There are hundreds of OpAmps that could be used. As I said, look for a low-voltage CMOS one which includes ground (Vee) in it's common-mode input range (called rail-to-rail in the industry).
The 4301 will work just fine, but is needs a similar power FET, it needs a special inductor, and a special Schottky diode.