Lots of great ideas here! I have a couple of things to add....
Don't hold the race in the middle of the desert...try to find somewhere a little bit cooler....
Make sure there is plenty of opportunities for some good scraps between lower powered bikes - only a very small percentage of ebikers have the time and resources to commit to going all out in an open category...sure, this is the race everyone's going be watching - the headlining act - but if you can work out a format that lets people race their lower powered stuff too, and still be competitive, then I think you will get a lot more people come along....maybe categories for voltage, or bike style, or whatever - i dunno. But if someone can come along and run what they brung, and still win a race, with plenty of time afterwards to kick back and watch the big boys go at it.....sounds like a blast to me.
LFP - I love your offer to fund it all yourself, and I can understand why.....it's your money and do with it as you see fit. But if you want to be generous, I think there are some clever-er ways to do it. Nobody would have a problem with contributing....I probably couldn't come out there, but hell, I would throw some dollars into this...this extra money could be used to do some really cool stuff, like funding airfare for some UK/European/Aussie entrants for example. Or money could go into an R&D fund for the ultimate racing ebike....if a bit of cash plus the resources on this forum could be used to develop a few bikes that consistently and reliably wiped the floor at gas bike races, we would see people turning to ebikes by the thousand....that would be extremely cool.
Also research and choose your date extremely thoroughly. I say this as someone who has some experience promoting hundreds of events myself....no date is gonna be right for everyone, but do everything you can to make sure its the right date for as many people as possible. I have seen many events failbecause the promoter didnt realise there was something else on that weekend....
J