1. Surface speed is in units (feet in inch mode) per minute. I'm not sure I follow your question.
2. As far as I know, there's no equivalent for G50 to set the minimum RPM, but you can program a G97 with a "target" RPM before you retract to the index position.
G01 X-0.03 (LAST CUT FOR THIS TOOL)
G97 S2500 (TARGET RPM FOR NEXT TOOL)
G28 U0 W0 (GO HOME)
N2 (NEXT TOOL)
G97 S2500 (TARGET RPM FOR THIS TOOL)
G00 X2.6 Z0.1
G96 S1500 (SFM FOR THIS TOOL)