Yeah and if he wants push on-push off, they have 10A push on-push off buttons on Amazon that could handle tbis job without even a relay to help it.

And they look cool too. And they're cheap..

 

Now, does he want a CONTROL circuit - ie something that will sense the temperature and automate the switching of the fans, or does he just want a SWITCH to manually operate the fans?

Sure. But why buy a mouse trap when you can build a Rube Goldberg machine to do the job? Lots more interesting and fun; don't you think?

Yeah, I guess you're right. Buying a toggle switch and wiring it in would be far more effective and reliable than trying to bulletproof a circuit against BEMF.

To answer the TS question, his circuit appears to be correct. Whether it's going to be sufficient or not - I'm not an engineer.

 

Isn't that what we should be aiming at, despite the attractions of weird and wonderful electronic solutions?

IMO, if it's possible, I think we should help the OP accomplish what he wants to do with what he wants to use to give him a higher sense of accomplishment. If it's not possible, or a lot of unnecessary effort, we tell him that.