0.65V is the approximate voltage drop across R3 in that circuit. You may also see it given as 0.6 or 0.7. Its exact value depends on the type of Q1 and on the temperature.

A 2 ohm resistor should give you around 325mA, if Q1 is a typical small signal transistor at room temperature. You can get 1.5, 1.8 and 2.2 ohm resistors easily, and 2 ohm resistors perhaps a little less easily. I think 1.8 ohms will give you close to 350mA.

FQP50N06L is a suitable mosfet to use (as are many others). 2N5088BU is a little obscure and you may wish to use something more readily available, such as BC547, BC337 or 2N3904. Any small signal silicon NPN transistor will do.

PS - if you want fine control of the current, then for R3 use a 2.2 ohm resistor in parallel with a second resistor of about 10 ohms. Adjust this second resistor to get the current you want.