The bike is sexy, congrats!
1) You should probably head to your LBS and try on different helmets. I personally like Giro Atmos or Ionos for looks but own a Specialized I bought a long time ago. Either way, look at a few helmets, try them on, buy what you think looks/fits best.
2) Jerseys come in different styles. I believe there's race cut, club cut, and something else. I don't really know. You want your jersey to fit somewhat tight to utilize the water wicking properties and for the aero benefits. Again, this is an area where you're going to want to go try on different sizes/cuts to find what fits you best.
3) Most blinky tail lights will work fine. I have a CatEye tail light and headlight. The tail light is a TL-LD1100 and I like it. The headlight is a CatEye HL-EL530 and it's decent but I'll probably look for a light that puts out some more lumens. Good lights can get pretty spendy so it's just a matter of how much you want to spend.
4) As for shoes, I'd agree that probikekit.com has some great prices but you're really gonna want to try on shoes before you buy them too. I recently bought some Sidi shoes online and the fit is pretty good but I wish I'd paid a little more, tried on some shoes at my LBS, and found some that are a better fit. My feet get pretty uncomfortable after a couple of hours.
Anyway, the moral of the story is that you need to go try stuff on for size. It can get expensive in a hurry so be prepared for to watch your wallet deflate a bit.