Three feet doesn't sound like that far to dig. After a couple minutes with a manual post hole digger it seems almost impossible to dig that far. I put about three inches of pea gravel at the bottom of the hole for the 4x4 to sit on.
I used pressure treated 4x4's from the big box store. After many hours researching online the best way to install 4x4's, I realized where the saying "ask 9 people how to do something and you will get 10 answers", came from. In the end I decided if these only last me 10 years I will be happy.
I used whatever wood I had laying around to support the post while I poured the cement. I poured the cement right out of the bags into the holes. I soaked the cement with water afterward. I have heard you don't even need to do that. You can just let the ambient soil moisture harden the cement.
Here are the post for the hops. They are 12 feet long, standing 9 feet tall. The Grape posts are 8 feet long standing about 5 1/2 tall and the kiwi post are 6 feet long standing about 4 feet tall.
This set up worked quite well. You can do almost anything with ratchet straps.
You have to feed and listen to this level. Its worth it though.
So here we are. I will post later about what I use for wire and how I plan on training the grape (middle posts) and kiwi (front posts) vines.
The hops will wind there way up the hemp I am stringing here. Next year at this time there will be a wall of hops where I am standing.