Where's the best spot to try a railway? Should I try it on a kicker first? when should I start my edge?
I would recommend to find a two-tower cable system like Sesitec System 2.0 and use shortening rope. The best length of rope is equal to height of tower. Also ask a cable operator to stop a cable system immediately after release (flick/scoop motion). When you land raley 5/5 times try to do it without stop of a cable system. The next step is to use longer and longer rope. If you do it without any issue it's time to try raley on full size cable system. So it's the fastest and safest way to learn it
if there is no possibility to learn on a two -tower system you should try it on shortenest distance between towers. Usually it's before the start tower on full size cable system.
The kicker raley is not useful in my opinion.
I agree that kicker raley will not help much, it will only let you learn how to land. But I would recommend to do raley dock start in order to practice the second part of raley - after release. What played most important role in my learning was removing bindings from a board (you could use wakeskate as well). This let me understand there is no need to edge super hard (you can't do that without bindings). Key is a very strong kick back with front heel while keeping leg straight in knee.
Personaly i would first learn it out of the water and i would start edging a bit toe side from the line.