I do pretty similar things as far as cleaning goes. If I need to, I’ll reach in with a sponge and loosen up anything that wasn’t removed by the hot PBW or oxiclean soak. Then I run some star san into it and push it through.
I do 5 gallon batches and use a small blow-off tube if I need it.
In my opinion, a 10 gallon corny keg is the perfect homebrew fermentor.
The Fermzilla All-Rounder is what I use for 5.5 gallon batches and a 14 gallon Kegmenter for 10.5 gallon batches. I can pressure ferment, spund and do a closed transfer to a keg using a floating dip tube. Break down is simple enough and cleaning is a breeze (I use a homemade keg cleaner set up after an initial rinse and dump). The vessels are unbreakable so far, so it looks like I am settled on these and I can get rid of any others or use them for bulk storage…
Spike SS conical. Easy cleaning, hard to scratch, easy temp control, pressure transfer, pressure ferment, spund, dry hop, harvest yeast. It can do it all.
One nice thing about Spike or SS BrewBucket is the trüb cone. Any break or hop material that makes it into the fermenter settles in the cone. Not sure it matters but I like that feature.
Otherwise plastic buckets (Speidel, Big Mouth Bubbler, generic buckets, etc) are perfectly acceptable. I’ve even seen some use plastic storage containers (aka Rubbermaid tub). The flat surface makes it nice for adding a spigot or thermowell.
FYI - if you’re looking for cheap kegs to ferment in, AiH has used 5 gallon ball locks for $40 and new for $90 as one of their Cyber Monday deals.