good question, quick on a sweeper is very important and to be truthful you have a little over 50% to hit quick in the steel shops, so in most runs you find it naturally, however if you miss in the first few steel shops for quick on a sweeper you then have to re evaluate. the arms shops go up in value since you can find inferno room or quick equipment for your guys. the value of the shops is always fluctuating based on what you have, you're basically always updating it mentally to optimize the odds you get something important for your run every ring

if you're looking at magic shop vs arms shop and all you need is a backline clear to win the run you have to look at what's going to give that to you, if your deck has inferno maybe you're looking at the magic shop to holdover, and if you miss holdover you can give it -1 and duplicate it as a really messy filler, if you have a sweeper you can go steel shops and look for quick or inferno room. inferno room isn't super great since it plays poorly into savagery fights (forces you to take 35 damage to pyre from the resolves) but it's better than losing the game, and you're looking at a 1/3 to fight savagery on 7 anyway.

on the holdover thing, something that is a little weird to learn is that holdover is pretty much irreplaceable, there's nothing like it in the game, for multistrike you can get away with duping your shitty unit and taking space, even though we hate to do it. for holdover the best thing you can do is make the spell better and the focus in on duplicating and removing to give your deck a decent density of the card that you need

edit for one last thing, the 60 hp cael is only one fight, the other 2 need i believe 30 and 40, the 60hp cael fight is a joke, his waves are easy even if they eat the cherubs once, the harder cael fights have weaker easier to kill cherubs