As with most things, it will somewhat depend on where you are. Even though California regulates pretty much every aspect of their residents lives, and think they rule over everyone else, most places are not California and have freedom to do a lot of things, especially when related to emergency services.
First, is this an actual helipad registered with the FAA, or just a department designated area for MedEVAC operations? I believe it is the latter, and if that is the case I would not treat it much differently than any other landing zone you use or set up. The only real difference from setting up a landing zone in the middle of a highway, or any other probable location, is the fact this is a prepared area, known by everyone involved, and likely with attention to limiting obstructions and other risks.
To the helicopter operator it is likely no different than any other off airport landing at a scene. If you can, bring them in to get their input on it. If not already, they will likely add it to their database as a designated LZ, including taking pictures and documenting other information.
As for the lighting question, what is the reason for wanting pilot controlled lighting (PCL)? Would not there be at least one representative of the department there as the landing zone officer? If that's the case I would suggest just having a hardwired switch that is turned on when setting up. This would also prevent inadvertent activation from other aircraft.
If PCL is really wanted or needed it could start to get a little tricky. Since it would only be receiving, there is no regulatory requirement for anything, but a frequency would have to be selected, and be legal for the intended use. Usually PCL is activated on the airports CTAF or UNICOM frequency. It may be beneficial to use the CTAF of a nearby uncontrolled airport since the helicopter will most likely be self announcing anyway. This would have the disadvantage that other aircraft could, and would, activate the lighting.
PCL is based off a number of key ups within a set amount of time, I think usually 3 seconds or so. The light intensity is set by the number of key ups, generally 3 for low, 5 for medium, and 7 for high. The exact configuration depends on the airport and lighting that it has. Some will only use a single setting, some will use them all, and exactly what lights are activated and at what intensity will vary considerably. If the nearby airport I mentioned does not use a specific number of key ups, maybe you system could be set to activate using only that one. That way both will coexist without the other being activated needlessly.
Since there should be a landing zone officer communicating with the inbound helicopter, there is a possibility of using this as a way to activate the system. It would depend on the type of communications system being used, of course. Simplex analog would likely be easy to set up, while digital trunking would not.
As far as the lights, most anything could work just as if at any other LZ, whether it be purpose built or not. However since it is a permanent LZ, I would suggest putting some thought and money into. Take note of if the helicopter operator(s) use night vision goggles and make sure whatever you use is compatible with them. Using FAA approved lights would obviously be the way to go, but can be expensive. This is where getting input from the operators can be very valuable and potentially save costs of fixing things afterwards.