This is actually what i use my memory seats for, one is daily driving, 2 is w/helmet. I am not as tall as you, and it can be annoying, use the tilt feature on the bottom of the seat as well to help buy some more headroom
Make sure you pull the seat forward a little for autocross, you want to ensure that you can easily push the brakes and clutch all the way to the floor, but more importantly you want the ability to really get on the wheel and drive (no gangsta lean...)
It helps to push the headrest all the way towards the back of the car as well.
At minimum put the car into competition mode when out there, i prefer just to shut stability control off though, as autocross has minimal damage if you do lose control, i would rather learn how to save the car/keep it from spinning myself.
General autocross advise i have learned -
Make sure to look ahead of where you are at you will end up going where you are looking, so you should be looking ahead to the next turn.
Take the first lap on the new course slow enough to learn the course, if you don't you will be looking for the fastest way around the whole time and never find it, nobody has their fastest lap on the first one, don't try to.
shift into 2nd and keep it there, there are few turns where you would need to put it back into 1st (and most of the time if you do, it makes the back end way to easy to come around
Put more air in your tires before heading out, 40 psi seems to work good (but i have not been able to experiment enough to find the preferred pressure)
On slaloms drive like you are trying to slap the back end of the car into the cone, you have to turn in earlier then you would think to really make it through.
But go out, have a good time if you can't do that you are doing it wrong..., and you will learn as you go, this is just the stuff i have picked up over the last few months, it has become addicting