With a bit of care, a steel rule should be OK, specially if you’re scraping by pulling towards you rather than pushing away. Your main problem will be if it’s flexy, you won’t get an even pressure, unless you’re very good with your fingers…
Best to do edges first, as little bits of metal swarf can get rubbed into the edge of the base.
A brush is ideal, but not essential, the frst couple of runs might be a bit sticky before the snow gets the rest of the wax out of the holes.
If the iron starts smoking, the wax is burning, turn it down.
You want to make sure the base is nice and warm, and all the pores are open, so once you’ve got the base covered, keep going from end to end, quicker and quicker, until you’ve got all the wax melted at the same time.
A good way of cleaning is to scrape the wax when it’s warm and then reapply, the wax pulls the dirt out and you get rid of most of it in the first scrape.
Wait till it’s cold on the final (or only) wax, stick it outside (not in the sun!) for a couple of hours. This means the pores close around the wax and holds it in.
This is stuff I’ve read, I’m sure some of is debatable (or wrong) but it makes sense to me and has worked well enough.