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Dave is right, of course.
Don't bother with the guide scope or computer yet. Align your astrotrac scope at home with everything assembled in your house or backyard, then on your next outing you can practice polar alignment. Coming from the Vixen polarie, I found the astrotrac scope difficult - be patient and persistent. You have to align the reticule, then you probably need to shim the mounting hole with a 1mm aluminum sheet; otherwise there is too much slop for anything but wide angle photos. I had a machinist make an adapter for the vixen polarie scope and I am much happier again.
For polar alignment, do you have a geared ballhead? Either that or the expensive single purpose astrotrac wedge. Don't bother going out with a regular ballhead.
You don't need a guide scope unless you are pushing the limits in focal length. With the vixen polarie scope snug in the astrotrac mounting hole, I can get a 560mm field of view and over 2 minute exposures without any guide scope.
Save yourself unneeded misery, if you plan on being out for a few hours, just get a dew heater and strap, and a portable jump start battery for it. You could try foot warmers and a ski sock, but that only works sometimes!