I just bought a 65 Fender showman on ebay, and I need a cabinet.
I found these 3 vintage celestion greenbacks G12M ( still 20 watt) for 20 euro in a garage sale, the guy didn't know what he had!

Now I have 3 questions:
1)
I have a newer G12M (25 watt), I can use them together to builded a 412 cabinet right? and the power rating of the cabinet would be 85 watt right? which would be ideal, cause a showman is 85 watt

Or is there a reason a 25 watt speaker shouldn't be with 20 watt speakers cause the power would be divided unevenly or something?
2)
Does any one know where to buy a empty 412 cabinet that don't cost 50 euro/dollar less then a filled up cabinet?
3)
I could make one, I have the equipment. I would use plywood, wich is the best, right? But someone told that after a while your cabinet start to vibrate, cause the wood is still moving a bit cause it isn't dead. And that would a small disaster.
Any one who can help me with these 3 questions, or has any experience.
Thanks for reading any way.