Quantum GIS (http://qgis.org) is free GIS software that might be able to do what you need. Bit of a learning curve (as with any GIS program), but there's a decent manual and lots of online tutorials and videos. Plus, once you learn how to use it, you'll know the basics for any GIS program. And yes, there is a Mac version available.
Doesn't matter, The native coordinate system for GPS is latitude/longitude, WGS84; if you save a location, your Garmin (old and new) will save it internally in that format. When you set a different datum on your Garmin, your GPS will convert from WGS84 and display the coordinates in the new datum, but the internal reference coordinates stay as lat/long, WGS84.
If you downloaded the waypoints from your old GPS with any program, they would have downloaded in lat/long, WGS84; no need to worry about datum shifts. If you have written down the coordinates in NAD27, then you would either have to convert them to WGS84, or enter them in your GPS with the datum set to NAD27; in the latter case, your GPS would convert them to WGS84 and save them in that datum.
- You don't want to scan the map at a resolution higher than is absolutely necessary, as this increased the overall size of the map. However, G-Raster has a "Rescale" function that will shrink an image down to a lower resolution to reduce the space required. My guess is that 200 dpi should be more than sufficient for these maps.
- If you can get the PDFs directly from MN DNR, that's a better choice, as they appear to be GeoPDFs that are already geographically calibrated. For your scans, you'll have to manually calibrate them either in Google Earth, or by using a "georeferencing" program. For both of those, the image will have to in a standard graphic format (e.g. JPG, TIFF), and not PDF.
- The largest image size the program can handle is 100 megapixels, which is convenient because that's about the limit the number of image tiles in Custom Maps for most Garmin units, 100 one-megapixel tiles (Montana units can handle 500 tiles). If your image is too large, there's a Chop/Crop/Shrink tool that can massage the image into a more compliant format.
- Read the help file; I've spent a lot of time on putting in as much info there as I could.
G-Raster author here. With the unregistered version, you'll be able to see immediately whether the program meets your needs. With KMZ files, it will show the center 1500 x 1500 pixels in full resolution, same with the upper-left 2000 x 2000 pixels for GeoPDFs. Just tested it on a PDF downloaded from MN DNR (Wellner-Hageman Lake in Brown County), and it worked fine. You'll need to run the GeoPDF tool first to convert it to GeoTiff format, then take the GeoTiff and load it into G-Raster.
If the TIFF from DNR is a GeoTiff (meaning it has calibration data embedded in it), the unregistered version will process the full image, no size limit.
I emailed the Forest guy in charge of the new compliance rules in April 2012 - he indicated that they were in the process of finalizing the maps to correct some errors. So if the date on the data is before 4/2012, then the data isn't current.
The Garmin map was created using MapWel. Loading the .img file into GPSMapEdit, looks like it uses a custom TYP file. It might be possible to pull out the road data individually and convert that into a transparent overlay, but it would be a pain. They're pretty good maps as-is, but they don't have contour lines or other features.
I contacted the Coconino when the maps were first released, and got a copy of a preliminary geodatabase file that contained most of the information; this could be used to create transparent overlays (separate out the individual components, convert them to shapefiles, then make a Garmin vector map). However, the version I got was a preliminary one, they pulled all links to the GIS data off the website, and I haven't yet asked for a more recent copy of it.
They had told me they might issue GeoTiffs of these maps, but they're currently only available in PDF format. You could always convert them to Tiffs, then convert them to Garmin Custom Maps format.
UTM coordinates don't necessarily reference true north, they reference "grid north", which can be up to 3 degrees off true north depending on where you are. I.e. if you walk a constant easting but increasing northing, you may not be moving directly towards true north. If you have your Garmin set to "True North", then it will use true north as the reference direction when measuring bearings and setting offsets.
Not directly, no. If you go to Page Setup and check the "Magnetic Variation" box, it will print arrows at the bottom for true/magnetic north, and the declination. Beyond that, your only option is to draw a track in the right orientation, but since the drawing tool doesn't show the bearing angle for the track, this will take some trial and error.
Well, the good(?) news is that the maps should work on your unit - not sure why they don't. The bad news is that they will be slooooooooow, much slower than the 60/76Cx models (and they're not exactly speedy on those). Go for the vector maps.
"Classic" Moagu maps don't work with the newer Garmin models; they take advantage of some hardware quirks in the older models like the 60/76CSx models, that the newer models no longer have. Maps created using Moagu's GUI for Bmap2mp will work on newer models, but Boyd is right - unless there's a really good reason, you'd be better off with those models using either Custom Maps or Birdseye imagery. Moagu is a hack intended for those who absolutely need raster imagery on their older Garmins.