Is an accelerometer suitable?

Other Hardware Sensors
1

I'm making a digital display for my car that will have ability to display acceleration, speed, ideally distance travelled (i.e. by successive integration of acceleration), and then ideally inclination and compass heading, altitude... that sort of thing.

I've sort of assumed that an accelerometer is the way to go, but I'm not sure if it's going to be accurate enough. There'll be local variations in gravity, variations in measurement due to changes in inclination that will be difficult to account for, variations in gravity due to change in height (though this, I'd imagine, is insignificant), and probably countless other things that I haven't considered yet.

I've also found this:
9 degrees of freedom sensor

This looks like it would be ideal, but it's a bit expensive for me, and I'm not sure it would solve those problems anyway.

Is there anything better I can use? Will the 9 degrees of freedom sensor be suitable?

2

There'll be local variations in gravity

No not that you can measure.
None of your other concerns are relevant also, but:-

and probably countless other things that I haven't considered yet.

Yes the noise on the output will make it impossible to measure distance or speed over more than a foot or so.

Is there anything better I can use?

I would suggest GPS.

3

You could also put a small magnet on a wheel and a hall sensor to get every rotation. That way you can get your speed and distance if you know your wheel size. But not sure about the lifespan with water, oil and dirt around all the parts.