And I'm done! 416 points. Great short-ish challenge, I'm definitely going to retry someday, only with four winters.
It took me 15 days, never thought it would be that long, even with only one book and all rewards/bonuses banned.
The biggest issue was the heat. My castaways suffered several heat waves and lost around five days, I'd say, where they could do nothing useful because heat strokes seriously deplete motives, and then it's a challenge to bring them back in a good enough mood that they will accept to skill, or just be able to skill, poor sims :D
I found out the hard way that with all EPs, and no sinks or ceiling fans (no plumbing and no electricity), water balloon fights are the only way to cool sims down. Swimming doesn't help!
Skill points: 17-16-13-14-15-17
I played on a beach lot, so most of the castaways had at least one Body point from swimming, and one Creative point from building sandcastles.