Very nice. The crankset change makes the bike look 'real' to me.

I don't like the stem, it's a steep angle not (the angle) -the type of quill.
I bought a threaded to threadless stem converter and run a stem with the removable faceplate.
The stem converter was 15$? used threadless stem -correctt angle 10$.

That bike, maybe an adjustable stem? I'd try to see if you can get your hands even lower. The lower and more areo (if your back can) the more speed you get.
As you notice I guess, your saddle no longer lower than the bars.

Maybe some new pedals?
MOSH or MSHBKS (Giant) makes some sealed bearing platforms (Half step bmx) that I got for $45?
Kinda look mtb, but really good pedals cheap!

Is the bb cartridge? if not -bearings, and in the headset too -replace and grease.
Really nice job, wish it was mine to tweak (you can tell huh?)
....

Are the brake levers mounted a little high?
I run my mtb levers pointing down to minimize the movement\effort -increase reaction time. That position seems like it would be hard to grab? And that lower would be easier?

Instead of crappy plastic reflectors, a little 3M refective tape front\back\side.
Plastic looks bad, nice you got rid of the dorkdisk, keep your limit screws on the rear derailer set correct.
Good job on keeping the cost down and the look factor up in the upgrade, I keep in mind when buying parts -that they might\can be used on a different bike as well. Build a bike of components and then flip the frame.
Some things wont fit -seatpost for example -sometimes the clamp of the front derailer.

Screams! -Red Koolstops!