The IRL540 datasheet shows a (relatively) high Rds of 77 mOhms at 5V Vgs so pulling 9 Amps through it would result in over 6 Watts dissipated as heat, probably need a heat sink. An IRLB8721PbF MOSFET shows Rds of 13 mOhms, only about 1 Watt at 9 Amps, May not need any heat sinking.
Can't comment on IMS-1.