For each race you can gain up to 16 points for coming 1st, with the amount of points gradually decreasing the lower you place.
Stage 7 has the same requirements as stage 6 to unlock, again you must gain 64 out of the 80 points available, but unlike previous stages there are now five races you can play in stage 6. This can be achieved by either four wins or a variation of placements as long as they bring you to, or over the 64 point mark.
Always aim to perform as many tricks as possible to give yourself an edge or more importantly even be able to keep up with the competition, but make sure you can these without bailing as that will seriously hinder your chance of achieving first place.