So essentially -- the BCS doesn't handle the power of some of the switches/instruments so you use an SSR as an adapter of sorts to speak between the BCS and the switches?
If you want to control burners, you'll need some sort of gas valves to turn the burners on/off. The gas valves (solenoids) that you choose will have some specified input. For example, some people use Asco valves that operate on a 120V AC input. What that means is that if you apply 120V AC to the valve, it will open. Disconnect the voltage, it will close.
The BCS-460 outputs 5VDC, which won't turn on the valve since they're not compatible. The 5VDC will control an SSR, which is just a relay or switch to turn on the valve. (nice analogy slimer
Your typical Love switch or PID may have an onboard relay that could output the 120VAC to the valve. The BCS-460, on the other hand, was designed to drive SSRs typically for high current electric loads. But SSRs are cheap, they can be used to bridge to the valves with a little wiring effort.
You'll also probably want some type of pilot light. I know that there are some really good threads, and people on this forum with a ton of experience with gas rigs that could point you in the right direction.