Hi Joe,
That sounds like a great choice! (I'm not sure there would be a bad choice though!
)
I can't help you with sourcing things too much as I'm on the wrong side of the pond.
I can tell you that Friends sells castings for the A3 drivers as well as castings for the cylinders if you're interested in those. They do ship overseas, though I don't know what it costs. here's a link if you want to look:
http://www.friendsmodels.com/productsforsale/kozowheelsdrivers.htmlI chose to do most of my A3 using mainly steel rather than brass. I did so for cost reasons, and because I was going to be paining everything anyway. The one other difference between the cold-rolled steel and hot-rolled, is that the cold is more accurate dimension-wise. If you order 1/4"x1" CRS, the dimensions are 0.250 x 1.000" (+/- a thou maybe). Also, I find the hot-roll harder to machine and it has an outer crust on it that has to be dealt with. But that is just my experience, which is somewhat limited.
I prefer the CRS and doing some stress relief before use, rather than dealing with the issues of the hot-roled.
Hopefully, you'll get some other input on this from those with more experience than me.
Kim