coming from experience, your second point isnt really a big deal. you will almost always be a few pixels behind on a persistent grief, the extra 5 to start doesnt really change much

it might be unpopular opinion, but the 2x cooldown for replacing previous pixels shouldnt even exist. you get into odd situations where greifers have advantage when your piece uses virgin pixels. but you can also use this 'feature' to cause more problems as a griefer if you are smart about it. find virgin pixels in the art space and place on those so you keep low CD but the repair crew gets double CD.

and then you have the issue where if you want to update your art, you get double cooldown for the new piece cus you are going over pixels.

overall CD should be the same regardless of what or where you are placing, it levels the playing field for everyone. this is not really a great solution to getting the canvas filled out when it can be used maliciously and repairing gets nerfed for it

a decent number of pxls regulars use a userscript to track timer on pixels 2-6. im unsure if there was ever any consideration to add that as a native feature though as its inefficient to stack pixels anyways so the extra timer is only useful to tell you if the next pixel in the stack is sooner than a full cooldown.