John:
Biggest thing – don't worry about what your friends wear, what Adventure Racers wear, or what anyone on this board wears. Hear the options but do try them on YOUR feet, with your socks, and decide what feels best.
Having said that, I live in NC – have hiked a good portion of the AT through this state. On just about all of it you can hike with a pair of trail runners or even street running shoes. I have hiked parts of it with an 800 series New Balance shoe. I get a 1/2 size larger b/c I feel my feet swell and I like the extra room. I'd rather have them too loose than too tight. If need be add a pair of socks. I lace my shoes very loose in the toe box and then tighter towards the top of the tongue – it's what works for me and I've never gotten a blister.
Now, it isn't my first choice even on the well-worn AT. Here's my answer to you:
1) I use Montrail shoes (Hurricane and Vitesse) b/c my feet are very flat as well and wide.
2) For me, the Montrail's seem to be wider in the toe box, are pretty light, and have a strike plate in the sole which keeps my flat feet from feeling more fatigue by stepping on the occasional rock, root, etc.
3) What also helps my flat feet is I will start my day with the insoles which come with the shoe, then after lunch I'll switch to a blue pair of SuperFeet insoles (the blue ones). Yes, I'm carrying 2 insoles but they're very light and when it comes down to it – now matter how light my pack is – if my dogs are tired every step is hard. Insoles do not take up a lot of room in your pack – it's worth it for me and it gives my feet a different "feel" halfway through the day and they do not seem to tire as quickly.
4) I have read that the Inov8 shoes are generally wider, are some of the lightest out there, and work great. I want to try them one day. Until then, I do like my system and esp. the striker place in the Montrails…
Good luck