There are some steps involved. First, each character requires a certain amount of points by Spring Break as you saw. If you look, there should be a stats button to tell you which ones you need. One will always be 150, another will be 100. The easiest way to do this is to find the job which raises the appropriate skill, as well as afternoon activity. Realize not all activities take place on every day.
You should shoot for 3 jobs during the week, and 3 activities at night/weekend (you can actually get 4 in, and on easy mode, money shouldn't be a problem).
Also, it helps to get plenty of sleep. I find myself doing more than the 3 naps, and sleep in twice you mention. What I usually end up choosing to do is pick sleep in on the morning activities, and then in the afternoon, pick the appropriate job to raise the desired stat. I also pick the evening activity to once more raise the appropriate stat. For the spaces in between I then pick 'Study' (the homework option). Just focus on the jobs/activities required to romance the specific person. Once you reach 150 with the other stat, then switch over, and get 100 for the secondary stat. This tends to keep the energy above 75% and this gives you bonuses for the evening and afternoon activities.
Note you will still want to continue raising these stats since to unlock the final CG, you still need 300 in the primary stat, and 200 in the secondary stat (and 600 to get the 'good endings)
No, you don't need to have 999 grades, but it is certainly possible to get. I sometimes substitute in a class session or two in the middle of the week.
The only person who really requires grade points is Anne. I think it is 250 before Spring Break, and then 500 for the final CG.
You also need to give them the appropriate Valentine's Day gift (which varies for each character). Anne requires the Old Poem book, Isabella will go for the Lingerie, Sally the Donation Receipt, and Rakesh goes for the Paint Set.
Also realize some characters require some minor additional steps. Besides Anne requiring gradepoints, you also need to successfully partner with her for the Prisoner's Dilemma.
