Tsukuba is an excellent choice. 10,000 isn't all that hard with a good setup. Here's what to do:
Get the Buick Special '62!
Get Comfort hard tires.
Set Spring rates (suspension) to highest.
Turn off all aids (except ABS 1, Active Steering on whatever)
Takes the turns SLOW and on the inside. Tap the emergency break button before every turn. If you go it right you will be telling the car to turn hard right for nearly all of the first turn but it will stay on the track (on the inside of the turn). Keep restarting until you get at least 3,000 on the first turn on Tsukuba- 6,000 is a possibility but not necessary to get to 10,000.
My best is around 17,000.