The general advice I like to give is to do the combine first and sort by age and height. Then if there are 10 or more 18 year old 1 and 2 ball players, do the group demo. Scout all the 18 year olds with heights that you like and interview any 5 ball players that show up (and 4 balls if you really want to spend a lot of points). Last time I scouted, I used 64 points, but you might not need to spend that many.
Also, as EBW said, you are probably ok only investing 2 points per week. There are 7 (?) weeks left, so you will get 14 more points, this will get you to 56 points, which should be plenty. At 4 per week, you will end with 70 points. I guess it really depends on the depth of your draft. I would scout all your 18 year olds and then see how many more points you need to interview the 5 ball ones. You probably don't need more than that.