I have used the post hammer thing and it works better than using a sledge hammer for fence posts, imo. The metal posts would be a good option, I would consider using them. I put in a 350' fence around our vegis garden but I used a hole auger on the tractor, it belongs to one of our neighbors, we sometimes use each others tractor attachments so we do not have to buy every one made.
Gumbo Sthil is all I buy any more, their tools work better than other brands some of the Husqvarana saws are also decent. I have 3 non-Sthil chainsaws I do not even use any more, a non- Sthil blower, and 2 non-stil weed eaters collecting dust. I do not have time for tools that do not have the power to get the jobs done. I do have a collection of Sthil saws, weed eaters and weed eater attachments, and power tools that get lots of use. Last year I got a Sthil 461R it can take a 32" bar, that saw is the one the local logers like the most as it is a chip tossing monster.
One thing I always do is take more than one chainsaw when I cut, if you cut enough times sooner or later you will find a way to get a saw stuck, mostly bucking them.
As the saying goes work smarter not harder.
My wife says I have a tool addiction but it is fine as they pay for themselves many times over.
The things I do are an evolution and I am always learning. My way is not the only way of doing things, and I may and will change the way I do things as I learn better ways. So any advice that I give is in that spirit.