That one should be easy to take care of if you scale the expected result (The 1 or 0 value) based on grid position. So divide grid start position by grid size and scale the expected result by that. This then takes into account stat position.
The car one is easy again. It would make sense that you lock servers down to a set car class TBO, GTR etc if you run a system like this. If not just apply rating comps when more than 3 people in same class and just rate them on their own in the same way you can have a race with multiple class cars.
As for experience, that is the whole point of the ELO/rating system in the first place. If little Timmy is good in the LX6 and not in other cars they will not get a good rating over time unless they ONLY race that car. The better you are in a higher range of cars and more races you finish the higher you will rise. The rating is just rating you against overs, nothing more. Only those that are consistent rise to the top and those that have a high DNF ratio will sink like stones.
It could also expend so you hold a rating for each car per person and theirr overall ating is an average of that. This way you have to be good in EVERY car to have the best rating.
The ratings build over time. Its not just a single race in the same way a race is not about T1. Its a long haul to make you WANT to finish every race.
Yep, ladder like but so is the ELO system. But its more subtle than that and most of all its automatic.
I like CTRA but if everyone raced enough they would all have highest rating. Here you get a bell cure that shows your true position compaed to others