The Wallas uses plenty of amps on start, but I do not believe they run through the on/off rocker switch. It has small gauge wires running to a plug on the board. So a 5a switch shouldn't be a problem in that circuit.
I think you still want to use a relay, though.
Radio Shack sells a real good one for under seven bucks that is almost bulletproof. Then you are only using miliamps in the remote circuit. I have several of these that have been in service for years, and the only time I have ever had one give up is when the 30 amp rating was exceeded.
Regardless of how you do it, you want to look real close at what the Wallas switch does. It is not (at least mine) a simple SPST toggle. There are an odd number of terminals on it - I think five - so it controls more than just the On circuit. That leaves you with multiple sets of contacts to control or having to leave the switch on, and breaking the main power feed. That is fine to do, but then you have more connections in the line they very explicitly recommend you connect directly to the battery. Plus you would then need the relay with possibly a latching circuit. You can put all the switches and connections you want in there if they are sufficiently sized and assembled so there is no voltage drop, but every added connection is one more request for a problem. Because of that, I wouldn't mess with it.
But the biggest reason not to start it remotely can be attested to by anyone who has ever had a flame-out on startup. Lots and lots of smoke and a mess made by fuel coming out the air intake (or somewhere) because the pump keeps running. You want to be there to hit the stop button pronto. It might never do it, but when it does it's ugly. The only time it ever happened to me was the first time I used Klean Heat, so that incident soured me on the stuff even though it was likely not the cause.
Nevertheless - if you really want a remote start, there is no doubt it could be done safely and efficiently. I think you should let DoD do it first, because all engineers go to a special school to teach them how to complicate stuff and are trained in the ways of covering their butts when the first plan(s) don't work out.
Calling Karl at Scan Marine wouldn't hurt, either. But I'm betting he'll try to talk you out of it.