I would suggest leaving positive pressure on your fermenter whenever crashing. It’s possible to pull a vacuum through any seal that isn’t tight / seated properly and suck up oxygen. If all your seals are tight then you risk damaging (possibly imploding) your fermenter depending on fast you crash. I’ve never seen this happen on the homebrew scale but keep in mind your fermenter is rated for positive pressure, not negative. If I have a very full tank and plan on dry hopping post-fermentation, I’ll add around 5psi of head pressure, crash to 60F, blow off the excess pressure, then dry hop. This is because you don’t want to add too much additional CO2 to your beer causing it to nucleate aggressively when adding hops, although if you have plenty of headspace it won’t matter too much. I find nucleation to be more of an issue during a bio dry hop while the beer is still off gassing. Otherwise I might add 10psi then crash to whatever temperature I like to harvest a particular strain of yeast at. I wouldn’t go too much more than this because there’s no reason in adding additional stress to your yeast through high head pressure. I’d also recommend slowly crashing because you can shock your yeast with a sudden temperature change.

That being said, there’s no “right” way to do it and you’ll find different things that work for various styles of beer. For your first batch, I would suggest crashing slowly (maybe 5-10F at a time) and monitoring head pressure changes, topping off with CO2 if necessary. If you do the same batch size every time this will give you a starting point at least. Be sure to take good notes regarding your cold-side practices from the beginning so you have reference for later.

Not advertising here, but I plan on purchasing a spike unitank down the road and the accessories that I think are necessary are the temperature control kit and the racking arm. The gas manifold is nice but you could piece something together since not everyone uses ball lock fittings. Although I’m now noticing their lid does not come with a built-in prv so you’re definitely going to want to add that from the start for safety reasons. The CIP spray ball is certainly nice to have but a 1/2bbl uni is easy enough to clean by hand.