Welcome!
Nope, it's a solid machine that you can putz around on just fine in stock form. Accessories only improve the capability and experience, dress it up, or otherwise cater it toward one's preferences. Best first accessory might be attaching a milk crate on the rear carrier for hauling stuff. If you do that, consider that the crate might mark up the paint. A dish drying mat or tool drawer mat can be used inbetween to prevent scuffing. Personally I recommend keeping any bike mostly stock until the first oil change, that's 600 miles for the CT125. Then you'll have a more informed idea of what you want from the bike. Many people buy the CT125, put a few miles on it, and then sell it - sometimes with tons of accessories already added.
There are however a few non-accessory items I'd recommend before you start putting miles on the bike. Many owners including myself have encountered a lack of dealer prep, so go over the basics of inspecting the bike, checking fluid levels especially oil, check chain tension, check throttle free play, check tire pressure off the lot, etc and make adjustments as needed. If you're a taller rider you may find that flipping the handlebar mounts or otherwise changing the position of the handlebar can help with ergonomics, and some owners don't like the stock position of the heel-toe shifter so they rotate it up 1 notch.
You'll find lots more in-depth info in the
Mods and Accessories section of the forum.