Maya, I want to wish you a good luck with this project, I am going to be watching this very closely.
in regards to your question re digital dash, I like the iphone/ipad Idea, but not so much on taking it off and putting them back on. unless you want to buy an Iphone and leave it there.
2 options that I think a permanent dash should have.
1. SLI-PRO - which then connected to a dash (your dash fitted with buttons and rotary knobs for rotary switch and rotary encoders similar to the one you saw readyfe has done.
here's what I have in mind.
I'm a big fan of that side look. I'f Im building a side dash box, that is what I'll built (kind of like Roy visser's one) check The way I play roy have a full built
Those buttons and rotary switch encoders is wired to control what goes on displays of the digits on the SLI pro,
another suggestion (that I am currently thinking of getting a liliput monitor my self and putting this in there) is the Zblue software . Z1 dash from Russell,
http://www.z1simwheel.com/dashboard/index.cfm This works with numbers of games. mainly rFactor, iRacing, rFactor2, gamestock car etc
I've had the software already, but using iSpeed as the monitor on iPhone with triples crashes the iSpeed app in windows. not the dashboard software.
it does maps (is live Map of where you are and where other drivers are in that screen) kind of like ingame but . out of your view so more like a RACE GPS if you will. or if you don't want that, you can change the view to the original dash (one for each car is made just like the real deal for the total of 29 dashes)
ie if you drive lotus 79, you get the dash of lotus 79. or HPD you get HPD dash. and you can change it at will.
another plus with this is also. some of the button that you built for the SLI-pro. if you are not assigning them to anything. you can assign it to control the Z1 dash.
Good luck buddy, I am very excited to see the complete result.