As for rental car . . .do you have the cash to rent or a friend to borrow from/ride with? If so, then it's probably not needed.
I think the split in liability is the number of people. 100/300 is $100,000 per person/$300,000 per accident. So, no split would be better, but whether or not it matters to you really depends on your situation. (Not to oversimplify, but are you worth suing?)
Remember comprehensive isn't about accidents, it's about hail, flood, stuff like that. If your car got hailed out would you actually get it fixed or would you just take the settlement? If you'd just keep the settlement then it's just $300 more in your pocket. Another way to look at the deductable question is that you're talking about spending $30-$40 year to protect/insure $300. Does that seem like a good deal to you? If so, then keep the lower deductable.
Hope this helps
