You've already decided on the first two, and you've already discovered that asking for advice on a couple of lenses to buy will return a list of at least a dozen. So, forget all those other guys and listen to me. (That was a joke; you can laugh.)
I agree that the one great walk-around lens for the 645 film cameras is the 45-85. It was the first and only lens I used with my NII for many years, but I tended to use that camera for paid stuff (read: portraits and events) more than for my own landscape work. Even so, for the full 645 frame, 45mm is reasonably wide.
The only reason to get the 80-160 in my view is that they are really inexpensive, even in the autofocus version, and for me fall into the "why not?" category. It would not be my second lens (actually, for me, it was more like my 10th or 12th 645 lens).
If you find yourself bumping up against 45mm too often, your next lens should be the 35mm. 45 is reasonably wide on the film format and something between 24 and 28 on 35mm, but for me it was wide enough on film for group photos but not for landscapes. Yes, the A version of the 35 has a better reputation than the FA, and the DFA is better still. But do not underestimate the quality of the FA version. Just don't expect it to give you 3-foot-wide prints used at wide apertures. That lens is a dedicated landscape lens for me, and should be reserved for tripod use at f/11. You'll need at least f/11 to get adequate depth of field anyway. 35mm is gratifyingly wide on the full 645 format (sorta like a 21 on 35mm)--I doubt I'd get better images with wider lenses, which I love to use but find the rectilinear "distortion" usually goes too far. But if you find that 45 is wide enough for your needs, skip anything wider until later.
After that, then I would consider a longer lens. There are two choices of note here. The first is the 120mm macro lens, which is simply superb. But don't discount the 200/4 FA lens, which is still not too long even for portraits on the full 645 frame (something like a 105 on 35mm). F/4 is fast enough at 200mm to use as a hand-held portrait lens, and for portraits the lens softens up just enough to favor the subject. But by f/8 or f/11--which you'll need anyway to get sufficient depth of field for most landscape subjects--it's critically sharp in my testing and experience. But the main advantage to the 200 is that it is tiny. It's a lens I'll throw into my daypack for a day-long hike without further consideration, even if I don't anticipate needing it. The 80-160 is a beast by comparison (though still not that beastly compared to, say, the 28-45 for the 645z). Get the autofocus version--the optics are newer and you don't pay enough of a price penalty not to.
But the advantage to the 120 is macro. it's a little short for a landscape telephoto--about like a 70 in the 35mm format. But the A version focuses at macro down to 1:1 without any additional doo-dads, and that is a big deal. And it is critically sharp when stopped down to an aperture that will provide sufficient depth of field. Like the 200, it's faster than the 80-160 and will do double-duty as a portrait lens, but if you are into gentle, smooth out-of-focus backgrounds with wide-aperture portraits, you'll need to be careful about what's in the background when you use the macro.
I'd rather have both the 120 and the 200 than the 80-160. All three are in the really affordable category.
Save your money for a good tripod, which will bring you far more improvement than the difference in any of the lens choices from Pentax. None of the 645 lenses are bad enough to really need improving when used properly, but all of them suck if the camera moves while the shutter is open, and it always will if you don't use a tripod. I spent more on my tripod (bought used) than probably what the camera and any two of the lenses you are considering might cost. I own about 10 tripods, all intended for professional use, and my carbon-fiber Gitzo blows them all away for lightness, rigidity, and smooth operation for cameras in this size class, even using a 400mm lens. Add a good ball-head (I use an Arca B1) and you'll never need anything better. That's expensive but a truly worthy investment. But even an old Star-D tripod, which my local camera store sells used for way under $50 in usable condition, will improve your images more than the differences in any of the Pentax 645 lenses.
If you had just gotten a digital 645, I'd recommend the 55 DFA, which is the (superb) normal lens for the digital format, just so you'd have something weatherproof to go along with the weatherproof camera. But the film 645's are not weather-resistant, so that is not a consideration.
Rick "an NII with a 45-85 is self-contained excellence, but a 200 in your jacket pocket will add a lot of flexibility" Denney
