Strength of Spring	Adjustment according to your leg strength is advisable. Like a pedal of a bass drum, if you make it stronger, you will get faster response. I think it will not affect the speed so much even if you adjust it loosely. I think my leg strength is not weak, but I adjust it slightly loose enough to express groove of my preference.
Gap between 2 Cymbals	It would be advisable to open more as you get more experience. If that is the case, your left leg has to adjust the gap between top and bottom cymbals. If you are not so confident in your foot technique, it is advisable to have less gap since amplitude range will be great. When recording takes place, you may adjust the gap smaller in order to get particular sound for the music.
Screw of Bottom-Side Cymbal	By placing the bottom cymbal with leaning angle, fitting of the cymbals will be varied. You can do this by tightening the screw for the bottom cymbal. To give your hihat a nice look from the audience side, it is advisable to turn a center axis and place the screw part on your side. It has a great impact on tone of the cymbals and you will get fortissimo. Also, it will affect the groove and the fitting.
Cap of Top Cymbal	Tighten the cap on the top cymbal and settle it on the center axis. Adjust the upper blurre by loosen the cap, then it will blurre while playing and make grooving and loudness. Just pay attention not to be out of joint while playing. Rikiya Higashihara's hihat is just great. He is the drummer whom I really respect. I call his hihat "Rikiya Hat".
Adjustments	Make sure to settle a tripod, a center axis, angle of the pedal.