As far as accessories, I'm simple there. I have a wireless computer with cadence (mine is a cat eye only because that is what the dealer had in stock), I little underseat waterproof pouch with a CO2 inflators, extra tube, and multi function tool with tire irons.

I always have computers wth cadence because I have had two operations on my left knee and one on my right. IMHO pushing a big gear at slow rpms is a great way to blow out your knees. I use all those gears to keep my old legs at 80 rpm, which works best for me. As far as brands on the other stuff, I just asked the salesperson what SHE would choose for her bike, and went with that. I have one of those little review mirrors on my sunglasses. Don't like it much, but I can't turn my neck the way I used to.

I also made a bracket that clamps to my handle bars and is drilled and taped for a water bottle mount. With that, my water bottle is up by my hands and I don't have to bend over to get it. I have no idea if they make an item like that, but I'd bet some one does. (I have a CNC mill and turning center, and I love to make stuff)

I did change my tires. The ones that come with it are perfectly good and you don't have to change them but I happen to love Michelin tires. I went the oppset of what most people would go on this type of bike. I went to a 700c x 25 pro4 endurance. I haven't been ridding for years, but back when I was riding a lot, I switched brands a number of times and ended up always going back to Michelin. I'm sure there are better tires out there, but I got a super discount on anything I bought with the bike so I got a set of these. I only put about 50 miles on the panaracer hardpack 38c tires it came with and had no complaints, I just wanted the smaller tires I was used to.