[Perfectlap]

it's always wise to take your time. But don't feel too aprehensive about jumping into a track day. You'll be in a large group of novices and it's slow going at first.
But definitely do it in the near future. You may need to sign up well in advance, allot of clubs have their novice events sell out quickly.

as for 75mph at an autocross, that's nothing uncommon. I think the law says you are not to surpass the local speed limit or whatever, but that's largely ingnored.
Here in NY/NJ we have a ton of clubs, not just national clubs like SCCA and PCA but some regional ones as well which were started because members wanted faster speeds, more open courses (fewer cones) and wanted more runs than the abysmal 6 or fewer that the NY SCCA has sometimes. Up here you have your choice any weekend of 4 or 5 events on the same day. Some guys do 40+ events a season.

But ironically those events (going above 75mph) tend not to be very popular because they favor the less nimble, bigger HP cars, result in very short lap times (under one minute) and are not very technical, far fewer turns. But I think its good to have some variety, one week its fast and wide open another week it will be trickier.
And if you are going into third gear which is good for 100+mph then its not really and autocross anymore.

at any rate.. think of autox as practicing at the driving range before venturing out for 18 holes. And depending on your club you can get some excellent instruction/advice for pennies when you consider how much your paying to learn 80% of the same stuff at a DE or driving school. And its really hard to learn all that in a single outing to a track or weekend driving school.