I think I'd start with that and see how well it cools before cutting into the factory wiring...

 

I agree. If those fans are pulling enough air to cool effectively, then they will pull too much power for factory switches. If it was me, one relay for each fan. On startup they pull much more than when running. So if one relay will run them, it will probably be overloaded when in startup.
Eventually you will cook something if that is the case. For instance my own 3800cfm fan will run on 40 amps. But will eventually cook a 50amp rated relay because it pulls 80amps on startup

 

I'd be inclined to agree, but curious as to where it plugs into the block & you'd lose the a/c trigger.

 

Then you need at least a 75a relay, which would take longer to cook (but a lot more expensive to replace) but preferably a 100a one; now they are pricey - but you'd only need one.

 

go with it. 160 seems kinda low, but try it.

 

Ok got this three fan system and shroud installed using the manufacturer relay running all 3 Fans but the vehicle vibrates when they are running. What’s that about ?

 

Out of balance fan blade(s) . If it's off far enough to shake a 3000 pound vehicle it shouldn't take too long to find out which one.
Trying to be more helpful....try disconnecting one fan at a time and see if that helps locate the bad one

 

Brother in law had a fan blade break off and lunch its way through the hood of his resto-mod pickup. Aside from the hood damage he said it was shaking so bad his fillings were rattling out. (Steel fan BTW)