I'm thinking about buying some a HUGE Blue food grade steel drums, which is either painted or enameled.
If I correctly modify them, will these be okay for FV, Mashing Tubs, Boil Kettle, Strike Boiler?
My concern is they are 205 liters / 45 Gallons
I would be concerned about their durability. They are likely not stainless steel under the finish so any exposed metal will rust. If you are planning on drilling holes for spigots, sight glasses, etc., that will definitely be a problem. Also, mash tuns and boils kettles take a beating with exposure to somewhat acidic wort and harsh cleaners. I assume you are planning a clean-in-place system with kettles that size? How well with the blue paint/enamel stand up to that?
Stainless steel is definitely more expensive, but it will last forever if used and cleaned properly.
I would not count on those being food grade. I recommend you look into 55 gal. SS barrels.