Hi Stoneage Harley,
Sounds like you've got quite the project with your Sportster there, and are looking for a display.
The first thing to keep in mind when using our displays, is that they are just that, displays. They'll display whatever ascii formatted data is sent to them very easily, however, you'll need some sort of controller to grab the information from the bike and transfer it to the screen.
I see you've picked out two 8x2 character screens, one with serial communication, and one with parallel. I always recommend going for the serial unit, in this case the LCD0821, as we've done a lot of the programming work required to run a screen for you. It's also got a GPO output on the back, which you could wire an LED to if you're looking for a simple shift indication.
As for your requirements, most of them look like they'll be dependent on the controller used. We do offer a start screen that can be saved so it comes on when the unit is powered, and it is possible to flash either the back light, or the entire display for that refueling indicator. You've also got eight custom characters you can create and save if you want to display a gas pump, or any other symbol.
Unfortunately, I can't be much help on the controller front, but I believe Parallax sells some of our products in their controller packages. There are many kinds out there, we use an ATMEL brand in our units, so look for the one that best suits your needs.
If you have any more questions regarding that project, just post them up and we'll do our best to point you in the right direction.