RE: swimming - Depends on the time of year. In the winter months, rarely, but sometimes Orlando gets frost warnings, so it might be too cold for even a Canadian, thoughI understand there are some of those polar bear club types who like that sort of thing.

I suspect when the weather is that cold they don't open them up, but I could be wrong. In early December, we had one day that was warm, and another where it was really too cold for swimming, several that were in between, depending on your preferences, but really only warm enough to swim in the afternoon for a few hours. I don't know about you, but in late fall, I'm just not very interested in swimming.
March is usally pretty safe to have good swim weather every afternoon, but maybe not at 9am. April - early November is pretty much warm enough to hit the pools first thing.
To the OP, it depends a lot on when you go. If it's a peak time of year, then getting there near opening time is helpful. But don't fret too much if you're there 15 minutes after gate drop, or even an hour, you'll still have a great day. You can also take the opposite approach - sleeping in and staying to close every day. It's practically impossible to go from 8am until midnight or later EVERY day of your trip (though we've actually come close once or twice....but most people don't last that long.) If you're hitting evening EMH then you really don't NEED to be there very early.
I've also seen the crowds fluctuate considerably. I think more and more people are taking afternoon breaks, so afternoons can actually be less crowded. 10-11 am seems to still be a peak time for crowds. Last spring we were at AK, it was madhouse busy. WE were thinking of leaving. most of the fastpasses were gone by 2pm. WE saw the FLK show, and by the time it was done, the parks had largely cleared out. It was amazing. After that, there were no FP, but the lines weren't bad, so we stayed a little longer. I'll wait 15 minutes for rides. We went on a late safari, and it was the best one I've ever been on (so much for the early am strategy...) Every day that we tried to take an afternoon break, the pool at our resort was very crowded.
With Epcot, it totally dpends on your goal. If you're touring the WS, then getting there early doesn't matter. Epcot has plenty of room too. AK used to be not crowded, but with EE it is more so now.