Hi Adam,
I've got a couple of suggestions and they are by no means aimed at you personally.I'm going to put them down line by line because I'm not(for once ) up for an essay right now.
It has been said many times here , everything has been thought of , lots of it done, some of it worked.....so find as much LSR history as you can...the good the bad and the ugly, the bold and the beautiful,look at 'em and read what they did.Some very clever people have been at this game, there have also been some mad ones and some very rich fools, learn from their experiences.
If you're going to be true to what you wanted when you started you first have to finish.This can be horribly expensive, if you bite off too much you'll have a half finished thing that has sent you broke.
This game is a battle between power and drag, you need to convince traction to be your friend. Power you can get at the shop,most people have more than enough.Drag is something your design will dictate and your design is prey to thousands of different factors.Keep it simple , have a reason for everything you do, not a hunch.
The rules. There are very specific minimum requirements related to safety, learn them off by heart and begin your design there. They dictate the smallest possible area you can sit in.
Learn the basics of aerodynamics, it's not likely you'll ever get to a wind tunnel so apply the knowns, the unknowns are bad science .
There are a lot of records up for grabs in the DLRA, but you're not the only person building something........have a really good look at the Budfab motorcycle streamliner, something along those lines is conceivable, aiming for 300 is a serious step for a self confessed newbie.
Go for it brother. If it wasn't for a shipload of naivete we would never have finished our car but that said I feel like the blind bloke who just walked across the freeway, I survived but I dunno what I was thinking when I started.