1) I prefer horizontal because it seems to be more versatile as to what you can fit in there. 2) I would stick to the pit calculator's recommendation because it's based off of volume of heated air to volume of the CC. 3) Yes you can use the same insulation. 4) I like the RF myself, it doesn't have a lot of different temperature zones like a traditional offset. Your top rack will be a little hotter than the bottom but end to end is pretty even, some guys like different temp zones so it really depends on your style of cooking. There was a build similar to what you are wanting to do a while back and the guy had an awesome thread on the build. I'll see if I can find it and post a link, it turned out to be a sweet build.
I found the build thread that I was thinking about but all of the pictures are gone now. The picture hosting service that a lot of guys were using recently changed something and a lot of pictures were remove from the forum. I haven't seen bkndsdl on here in a long time so we probably can't get him to repost them.
The only thing I would add to what BigT said is the calculator isn't designed for verticals. So if you did do vertical the FB could be smaller but, if you want to burn wood only I would have an Horizontal CC. Because a vertical would be best for charcoal or vented CC so things didn't get too hot. This can be done a couple of ways but it is a balancing act you may not be happy with.
Current Smokers: Backyard RF Offset and Hybrid RF Offset trailer rig with Cowboy cooker and fish fryer, always room for more........
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