Does the enlarger come with a metal wall? I ask this as the norm in many darkrooms with these kinds of enlargers, was to have a metal wall and one used magnets to hold the paper up, best way to hold paper vertically.
I seem to remember 360mm lens as a standard on the two 10x10 horizontal enlargers I have personally used, and something like 460 or 480 for very big projections.
Does it run two banks of 250W lamps down each side? Total of 2,000 watts in the head. If so and you blow a lamp, then replace (preferably) all 8 lamps, but I would suggest a minimum of the four lamps on the side that blew a lamp.
This was mainly for colour work as if one globe blew, then the others would start to be getting weak and would have a substantial colour shift generally, so we replaced them. With B&W not as big of a problem though.
You'll wonder how you did without it once you have it up and running.