2 Don't shim the needle.
3 Maybe. It is likely your spark is not the strongest. It can be checked with a spark stretcher and/or check the voltage coming from pin 9 while cranking the motor over. Tell us what you have.
4 You'll run on the idle jet through idle, choke and off idle. These are the three holes you found blocked under the butterfly. They may not still be entirely clear. They are .5 mm and best cleaned with the plain end of that size welding tip cleaner bent 90 degrees at the end. You may have these clear, but not clear enough.
5 What is your air filtration?
6 Are the springs present on top of your piston slides?