Like Mad Dog said, unclip WAY before you think you need to. Also, you need to identify which leg you want to make your plant foot and which you want to leave clipped in. I always leave my dominant (right) foot on, at the 6 o'clock position, while planting my left. It's the easiest, most coordinated way to get back up to speed from a stop.
Personally, I would recommend having someone put some basic platform pedals on so you first get comfortable simply handling the bike, getting acclimated to riding "in the wild", working on developing things like listening for cars, anticipating lines for turns, etc. Trying to incorporate those things with the nagging knowledge that you are also clipped in may prove not so good. I road platforms my first two seasons before going from a hybrid to my first road bike, and I am a much better rider for it, getting hit by buses notwithstanding.
馃槜
As for the tires, 25s should be fine. I ride 25s, usually with around 110-112 PSI rear, 90-100 front. I'm same height as you, average 220, give or take 5 lbs for what point of the season it is. Never pinch-flatted once. The 28s will be cushier, make sure the Synapse can handle 30s, especially Contis as I've heard they run wide (I run Schwalbes exclusively).
Speaking of which, learn how to change a flat (and try a practice run) before you actually get one. Also, get yourself a seat bag with the following: spare tube, patch kit, tire boot (or a small denomination of currency), bike multitool, CO2 inflator and cartridge. I also carry a small mini pump on my frame.
As a relative newbie, I can say I totally understand that all this can be overwhelming (and I left out quite a bit), but once you get it down, it's awesome, and absolutely worth it.