In regards to issue #1, you have broken the rules and shouldn’t park on common property regardless of whether it’s in the way or not. You have been told not to park there but I do feel the way you have been approached is in a way classified as bullying – I’m glad you have said that you don’t want to be approached in that way again.
As for issue #2, there is probably a limit set on how much the EC can approve. This limit is set at the AGM. I’m in a complex of 14 and a limit of $15,000 has been placed on the Executive Committee’s powers for the coming year. There should have been notification about the signs and changes to the letterboxes. The EC should’ve had a meeting about this and the Agenda & Minutes should’ve been placed on the noticeboard. If the works have had a negative impact on the look of the common areas and you weren’t informed beforehand, I think you should look into this as it may lessen the value of your lot and in that case the entire OC should have voted on these changes beforehand.