Should I pack the u joint and the steering gears tight with grease like a wheel bearing?
Yes. The steering gear will stay greased for a long time while the u-joint may need frequent additions of liberal amounts of grease to stay filled up and to avoid oil leaks from the fourth main (if it's worn).
I go a little sparingly with grease in the steering gears. Too much and it will ooze out of the threads and make a mess all over your nice clean pants.
What Ron said!!
Ron and Jerry are correct. I overfilled my steering gear, and every time I reached in to adjust the spark and throttle after starting I became Mister Greasy Hands.
^ would Teflon plumbers tape be a good idea on the threads of the steering hub?
My opinion is the plumber's tape probably wouldn't do any harm, but is really not necessary as long as you don't pack the steering gear case full of grease to the point that the gears pump it out every time you turn the wheel.
Make sure that the locking screw is installed and tight after working on the case so that the case cover can't rotate when you turn the steering wheel!