I am recommending that you read the Corky Bell Book
Corky Bell "Supercharged"
Sea level is good, you will have more power and probably can get good gas (93 octane). Don't even think of running lower octane.
Sea level is bad, it could push your fuel system to its capacity limits.
The issue here is that you will be increasing the fuel demands on the existing fuel system without any instrumentation to verify that the fuel system:
a - has the capacity to support the increased requirement
b - is actually providing the increased fuel
I don't think you will ~ need ~ to get different injectors initially, and I would suggest that you don't, assuming that you are able to check the function of the fuel system. The best method to do this would be with a wideband air to fuel meter. This device will tell you what you A/F is real time.
The JRSC installation manual instructs you to check the fuel pressure for the dynamic rate fuel pressure regulator. This method of fuel management is "dumb" because it simply increases the fuel pressure at a 10:1 (relative to manifold pressure) ratio when in boost. While this is a crude method, it does achieve one benefit; it increases the capacity of your fuel system by increasing the fuel pressure.
The voodoo box on the other hand uses a superior method of increasing the injector on-time. This allows the injector to exhibit more predictable and linear characteristics because the pressure differential across the injector remains constant. Injector behavior changes with differential pressure. The Voodoo box does not however increase the capacity of the fuel system. So for instance, if the stock ECU is commanding 80% of the available fuel capacity (which is a measurement of time -> read book) and you need an additional 30% of fuel, then you will run into two major problems. First, the injectors only have 20% left to give, which will run you lean and could cause bad things to happen, and second, you will run the injectors at a duty-cycle that will exceed their ability to dissipate the heat that builds up in the coils, potentially causing malfunction.
So, what do you do?
Check the fuel pressure. Old fuel pumps and old pressure regulators can wear out. Charging/Battery system degradation can reduce the fuel pump's flow rate for a given pressure. Sans a manifold pressure reference (see boost gauge) you will have to be organized about how you do this. We can discuss later if needed.
Set base timing to 6 - 8 degrees.
Install an aftermarket fuel pressure regulator. Adjusting the fuel pressure can get you a higher fuel capacity with your otherwise stock fuel system. Play around with the calculators here:
Fuel Injector Calculator from WitchHunter Performance
to see what that means.
When you can, instrument your car. I am a huge fan of instrumentation. The base instrumentation would be the A/F (wideband), manifold pressure (Boost), and Fuel pressure. The fuel pressure doesn't even need to be piped into the cabin, but it is a lot better that way.
I know this seems like a lot, but I promise if you read that book, it will not seem so daunting.