Agree with Velo, NY Biker, and Murienn.

Helmets need to be tried on your head because different shape heads feel differently with a variety of helmets. Some people like having a visor to their helmet to block sun. Others say the visors block visibility, especially seeing traffic lights ahead. Most people like being able to have the ability to adjust the helmet tightness which most but not all helmets have.

I don't like bibs because I pee a lot and bibs are annoying. I like the brand Aerotechdesign better than my much more expensive Pearl Izumis.

As for the bottle holders, I like the ones that are shaped like wings. I hated the ones from Specialized which made it hard to pull the water bottles in and out. I like my Podium Ice bottles, but since they are slightly wider due to the insulation, you might want to check how they fit in the bottle holders in your bike. Also, I had to get the shorter/smaller size because I have a 48cm bike and the smaller ones barely fit on my bike.

As for the bike bag, I like the ones that can unzip to enlarge if you want to. I also recommend trying the bags on the bike because saddle bags hang slightly differently on every bike. I would also try stuffing whatever you want into the bike bag to decide which size to get. Some people are minimalists, where they just have one tire tube and a cannister of air and 1 tire lever. Other people want room to place extra energy bars, bike tools,Motrin, bandaids/abrasion neosporin sprays, tubes, air cannisters, maybe even squash in a thin pocket-sized rain jacket.