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Sorry to see that. Glad it didn't turn out worse. That's a major reason I avoid urban bike riding and keep it to gentle mountain biking where I won't encounter any vehicles aside from other bicyclists.
So I don't actually technically own a bicycle at all right now, hopefully will be getting my first ever road bike tomorrow or the day after, a 2016 Cannondale Synapse Carbon 105.
However the shoes did arrive early today, given my wide ass feet and being Australian went for some Bont Vaypor S, now just need something to wear them on.
Very nice choice for your first road bike, excellent frame/geometry and the 105 groupset is an amazing bargain for the money, really excellent.
Have you ever wore clipless shoes before?
Never, which is why I'm going to head to a nearby park where there's a soft landing to be had until I get them figured out...
Any tips?
Tips? Yes, sir....unclip well prior to coming to a stop at a sign or a light...don't wait until you're ready to put your foot down at the sign or the light. Don't ask me how I know this! 馃榿
Never, which is why I'm going to head to a nearby park where there's a soft landing to be had until I get them figured out. The bike is used (barely) and has 105 pedals on it so it'll be SPD-SL which at least seem pretty reasonable to understand compared to some others. Also thinking of switching out the OEM 25mm tyres for some 28/30 Continentals to make it a bit more heavy rider and grass friendly.
Any tips?

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.