yes, not all 360mm rads are equal so which one are you looking at and with what fans. An 80mm thick rad with Deltas will cool great but you won't like it.
Yeah nah. The 3090 needs more than or equal to a 360 rad on its own if you want better than the stock cooler for air...
Isn't the rule 120mm rad a space per 120watt of power?
Are 80mm thick rads even a thing?