I bought everything all at once because I had a 0% APR offer when I bought my bike. It was the bike, pedals, shoes, computer, and bottles and cages. I didn't need anything else, really. I like my pedals but there was a learning curve. However, within a week, I was fine with them. I just needed to spend time in a church parking lot where I had to breathe calmly and ride around. I then tooled around the neighborhood and didn't get hurt with stop signs there. Before I knew it, I was a pro. I second the "buy platform pedals or go clipless" route. Even better (in my opinion) buy pedals that can be platforms OR clipless pedals. That gives you the opportunity to go clipless. Once you do, you won't want to go back for long rides, but they give you flexibility. I commute on the same pedals that I ride long rides on but I wear tennis shoes on the platform side most days because of university traffic being frightening while maneuvering with full panniers. Throw in being clipped in and it can be an issue.

As for the bike, just get what you are comfy with. Get fitted properly and you're good to go. No one is going to say "Oh God, that's a bad bike". Everyone has preferences with bikes. And if people do, they aren't worth your time. But seriously, I have never in three years of riding road bikes seen that Cyclists are good people for the most part.

The computer is invaluable. I third this. I have been through two now. The one got burned up in the Missouri summer. I've never paid more than $40.00 for one. They're cheap and effective. The guys that actually ride crits at the store recommend the cheaper ones. Putting ones that require cadence on is a pain. I recommend you have them put it on for you when you buy the bike because they are a bit of a PITA to put on yourself. I do my own maintenance now but putting one back on after taking wheels off and truing the back up after a brake malfunction was a pain the first time. You'll just want to enjoy your bike at first!

Have fun and just go out and ride!