If you have runs in your epoxy, you're putting on too much.  Exactly how much to put on - enough to do some good, but not enough to run - is not easy to determine when you're working.  Lots of experience helps.  I've been doing it for many years and am getting better at it.  What really helps me is to go back and look for runs an hour after applying, especially on vertical surfaces.  Then another check in another hour.  If I haven't caught all the runs before the epoxy turns green (means it's still a little soft, not rock hard), I use a scraper to attack the runs.  I use slow hardener at shop temps in the high 60s, the epoxy is green in 12-14 hours.

Good luck on the rest of your build.

When I started using an almost dry roller rather than a brush, I got fewer runs.  But in tight spots, or in other cases, a roller can't be used, and I still need to use a brush. A simple cabinet scraper does work very well for planing off the offenders.

One thing I've heard but haven't yet tried is warming up the resin and hardener before mixing, to reduce the viscosity of the mixture.  That's supposed to make it easier to apply thinner coats.  The warmer it is, though, the less time you have to work it before it starts to turn to gel.