I'd absolutely recommend a camera that utilizes an electric release instead of having to engineer a solenoid on a standard cable release socket. Your Nikon F4S should work well as it has an electric cable release (2-pin, easy to splice into once you have the right connector) and OTF flash metering. You really don't have to build a triggering device yourself, but will need to splice a jack into an electrical cable release.

Several retro-reflective NIR triggers are available commercially that will do everything you need and cost less than $100 each. You'll likely want two for a crossed-beam trigger array for pinpointing composition and avoiding false triggering. (They're wired in series so that both beams must be broken simultaneously in order for the camera to fire).

I use SecoLarm Enforcer devices with sub 10 millisecond latency, that draw only 20 milli-amp-hours of juice off 12 VDC (run off AC or DC over a wide range of voltages down to a minimum of 10.8VDC) are waterproof and about the size of a jumbo pack of chewing gum.

There are a bunch of similar devices nowadays but the Enforcers are especially nice. Used with film cameras and flash as they won't run through a whole roll of film once they lose power, as will several units I've used in the past. And while they are self-contained with their own IR light source, they can also be used to detect red LED laser pointers substituted for the reflectors.

I use Quantum Turbo 2x2 battery packs for powering up flashes for several days. These recycle a full pop from a Nikon SB800 in one second. If you dial down the flash (and use several) you can keep up with motor-driven sequences. To avoid eye-shine, take the flash off-axis. Use the widest lenses you've got.