Privacy Fence Post Hole Questions

Hello! I'm replacing my 6' privacy fence in a few weeks with new posts and 6'x8' dog ear pressure treated pine panels. Looking for expertise on post hole digging and if the below method is sound per post - my frost line is 24" deep:

• 28" deep holes
• 8" diameter for 4x4x8 posts
• 12" diameter for 6x6x8 posts (2 for gate only)
• 4" of gravel per hole, post in-ground for 24"
• Dry concrete topped with water, unmixed

I've read no need for gravel, no need for cement, both needed in each hole, one or the other needed every other hole depending on run length, etc. etc.

I'm replacing the front and back fence, front is 33' with a 10' gate. Back fence has no gates, but is 100' long. Planning on about 17 posts in total.

The sides were taken care of by the neighbors, as the elderly woman who used to own my house could no longer take care of the front or back.

Let me know of what additional info I can provide! Just making sure I'm not over-planning OR making a fence that will blow over/rot/etc.