Cool project, did something similar a while ago.
I would not not use pulseIn fo reading the Rx. You need to write a custom handler and read the radio 3 times. I found the arduino can "jump" around in the values. By reading 3 times and taking the average you get a much better read. Would hate for a small glitch in the timer or something else cause the retracts to suck up or go down. The timers can be querky especially if you get a clone unit.
I originally made a sequencer for my canopy on a turbine jet using an arduino. I evnetually switched it over to a switch instead. Didnt want to chance it opening in flight if I bump the switch.
https://www.google.com/url?q=http://...Hspz5sNwhebllw
I also used an arduino to operate a custom turreton my b-25 with random 360 degree motions!
https://www.google.com/url?q=http://...g2ULSmfMCNrrEg
These are real fun to play with but I just cant trust them yet in a turbine aircraft for the landing gear.