Hi James,

will be cutting dozens of 6 x 6 beams, so could cut down on work
if we had a saw that can cut in one pass.

I would just use a normal circular saw, making a cut on one face then
flipping the beam over and completing the cut. This will produce a
cleaner and more accurate cut than a chain saw, and will be a LOT less
work than trying to lift a beam into position to cut with a power miter
saw (if you could even find one that can cut that big of a beam).

If you're really concerned about the appearance, you could clean up the
end after the cut using a hand plane, sharp chisel, or a belt sander.

stake them in the ground with rebar. Will nail beam squares together
with 10 inch galvanized spiral nails.

If it were me, I would use long screws instead of nails. Most home
centers stock landscaping screws like this in their hardware area. A
driver drill would have no problem driving these.

For the project, it will require a lot of drilling. Thinking about
buying a basic drill press to drill pilot holes first.

I think most of the landscaping screws are self tapping, so you wouldn't
need to drill pilot holes. But for the rebar (and pilot holes if you
choose), just use a good drill with a long drill bit (self feeding bits
help if you can find them in the size you need). You don't need the
accuracy of a drill press for this application and it would be a lot more
work trying to position a large beam in a drill press anyway.

I have a DW246 drill for these kinds of tasks. It is small and compact
but very powerful. With a 2" self feed auger bit you really have to
brace yourself or it will rip your arm off if it hits a knot or
something.

http://www.amazon.com/DEWALT-DW246-2.../dp/B00002233G

Am building outside steps on a slope, in the mountains.

If that's the case, you certainly don't want to haul a power miter saw
and drill press to the area and try to set up work stations for each
machine out in the dirt and rain. These are shop tools, not remote
mountain tools.

Of course, you will need to figure out some way to get power to the site,
even with the portable circular saw and hand drill. If you are close
enough, you could use heavy gauge extension cords (10 gauge) to go a
couple hundred feet or so. If you're farther than that, you should
probably buy or rent a generator.

Alternatively, you could use a cordless drill and saw if you have lots of
extra batteries.

If you don't have access to power and don't have cordless power tools,
you can always do it the way our ancestors did. A handsaw and manual
auger drill bit. It's slow and laborious, but it works.

Will build "squares" out of beams

One final thought... Have you considered prebuilding your "squares" in
your shop, then hauling the finished sections to the site? You could get
really fancy with the joinery if you wish, half laps at the corners or
mortise and tenon if you feel it's necessary. Build everything in your
shop to get the accuracy you're wanting, then you would only need a
hammer, shovel, and cordless drill on the site to fasten them in place.

Good luck!

Anthony Watson
Mountain Software
www.mountain-software.com