For the front, should I just take the whole wheel bearing unit out, bang out the broken one and tap in the new one?
And for the rear, what should I do?
And last question, are they the same length(front and rear)?

Just get replacements from your NAPA store or whatever. Front and rear were the same on my 98. Remove brake caliper if there'* no room to remove stud by hitting it sharply with a hammer from the outside.
Place new stud in from back. Tap it gently with a punch to start it in hole. I used 5 washers on the stud and then the nut and tightened the nut with a socket to pull the stud into the hole completely.
Remove washers. Replace wheel. Torque bolts to spec. Drive short distance. Recheck torque.