I think you're on the right track for mowing - the ztr is the best mower, keep it and use it.
I'm with you on the truck, I use mine only so much any more but I wouldn't be without, living in the country.
I personally would look father at other tractors as well. A well-built tractor shouldn't need much other than typical maintenance, and you sound up to doing that yourself. My dealer is 100mi away, and in 4 years my tractor hasn't paid him a visit. I did blow up my radiator (my error) but it was easily field-repairable.
On that note, there's a lot of other brands which may suit you just as well. After much research, I ended up with a Branson; others like Kioti, LS, Tym, besides the prevalent Kubota and Deere. As far as I can tell, they're all of similar quality (I'm a bit more than 100hr/year for 4 years now and other than my mistake hogging in the heat and not watching my chaff screen & radiator, zero issues) though some are definitely more heavily built than others (guess which) and you'd be *amazed* at some of the price & feature differences (same heh).
Someone's going to tell you to buy a trailer to be able to take the tractor somewhere (to the dealer, probably). Don't. You can always rent one if you really need to, and you can do a lot of renting without getting anywhere near the price of even a used trailer. Also if you have no trailer, you can't take your tractor to the next county over to help someone...
Backhoe: I got one. It's occasionally used, and I love it when I have to use it. I rented a TLB "locally" (an hour roundtrip from home to rent it and bring it back) so I knew what it could do, and I like being able to put it on or off (5-10min) to do a quick job that would take me all day + a backache (it stays on the tractor until I need the 3ph, then it stays off till I need it again, etc). Yes you can rent, but you won't rent for that one job, and it's tough to wait on jobs to be able to do them all one day when you do finally rent. Big downside: adds about $6-9k, so think that one through well.
Post hole digger: great for fences, maybe ok for trees unless you want more than a 10-12" wide hole... and if it's rocky, a phd is going to have a tough time - a backhoe can work around the rocks and get them out while the phd will snap the shear bolt and say no.
I have to echo the "$200 for a plow?" - each snowstorm? Or all winter? Or is that for driveway maintenance?