I'd be looking more in the 50hp class of machines in your shoes
I've got an old
l2250. it is a bit smaller than the 3400 (about 8hp down), but not so much so that I can't speak to your situation. the hobby farm in my case is much bigger, but we only have about 1 acre for a fenced off garden. we do some logging and road work with it. In the past we've moved plenty of large rocks and snow plowed. it was too little machine for what we were doing with it. now those jobs are being done by a dozer and a truck mounted plow.
the back-hoes on that sized machine aren't super useful either IMHO. the reach isn't long enough, and you end up having to move constantly to get the job done. Moving around that much, you might as well use the bucket most of the time. I'd almost say the best use of the backhoe has been as an adjustable counter weight, and an occasional self-unstucker.
now the most common jobs for the Kubota are dragging logs out of the woods and loading gravel into the back of dumping pickups. Both could be done easier with a larger machine.
as for tilling, it takes a while and works the tractor hard, but we have much less land for dedicated gardening. heck, I used to till over a half acre as a kid with a walk-behind before we got the 3 point tiller.
Its better to have too much machine for the job and end up working the machine easy, then over working it and constantly breaking it. you also wont necessarily save any fuel with a smaller machine, unless you are joy riding or idling quite a bit. If your work has you putting say 75hp-hrs into the ground, it doesn't matter if its 75hp over 1 hr or 25hp over 3 hrs. If you end up having to go back and forth several times working it hard vs. 1 or 2 passes of a cakewalk for the larger machine, the smaller machines can even burn more fuel.
I was once considering buying a semi-tractor, and figured a smaller engine running at higher boost and an automatic tranny might save me some fuel, even more so because I could get them with a smaller cab and chassis. My friend, and engineer at CAT said "good idea, but it isn't so." The manufactures figure the customers for the smaller engined machines weren't as picky about fuel efficiency as the big guys, so the big engines are actually more efficient.
be careful about your assumptions when it comes to stuff like this.
ps. Hydrostatic drive is MUCH less efficient than an old fashion gear drive