New member! New bike! New... mechanic?

Yep, blue arrow is the blanking plate over the mixture screw. It needs drilling and removing, a very easy job. It's well covered on the forum elsewhere. Essentially it's this:
- Take small drill bit (3mm ish)
- Drill down into the hole in the brass blank about 3 or 4 mm (dont push hard, it's very soft metal)
- dull the tip of a suitable self tapping screw
- insert the screw into the hole
- turn it until the blank spins then pull it out

The red arrow is where a ball bearing and small spring live. Theres one set per carb. The are held by compression on the rod and the balls act as the detent setting for the choke rod. It will help you to have it as you can set choke much better with it in place.

The plates:
The upper one with the crank and tube is the throttle cable retainer. The lower one doesn't look familiar at all ...

Nice to see you making progress