A 4-flute is going to load up fairly easily, while a 2-flute is much weaker. Have you considered a 3-flute?I have machined quite a bit of alum bronze, but not with an end mill this small. It will be 4 flute, and suited for the material.
Otherwise, budget for some spares while you learn :-)
Oh yes - spindle runout and shake can be a problem that small.