What is the minimum power and size (and/or other considerations) I can get to do resawing? I am thinking the pieces would be big as a piece of firewood. I guess it could be a little bigger. I don't know. I was just kind of intrigued by the whole resawing thing.
The limit in size you can resaw width and height-wise is established by what size wood can fit through the exposed blade area of the bandsaw, so measure the distance between the blade and the support column that holds the upper blade wheel and the length of the exposed blade and you have your maximums. Length-wise, of course you can go on forever, provided you can support the wood in order to feed it through the blade.
Proper support becomes more challenging as the board/log becomes larger. The wood must pass through the blade without twisting. You are trying to cut bread slices from a loaf and any twist in the slice will result in a more difficult milling job with a the jointer and planer including much greater waste. Twist is also very hard on the blade and can easily cause binding and breaking of the blade due to the increased tension it provides.
When I resaw previously rough sawn lumber I can support it using portable roller stands before and after the table. For log type resawing work I have rigged up a long roller feed that replaces the bandsaw table and has a mounting sled so that the log can be securely anchored to avoid any rolling to the side as the log is fed through the blade.
As for power, my bandsaw has 12" of exposed blade and 14" side clearance to the column, is 1 HP and does fine with hardwood logs up to 12" high, although the feed rate is very slow (I'd guess approx. 1/8 to 1/4" in 10 seconds).
There are other tricks to resawing so watch some videos and/or get a good bandsaw book to get more insights. OR come back to this site as your questions arise!
I have resawn up to 6" with a 14" band saw with a 1/3rd hp motor, painfully slow. A good resaw blade makes all the difference. All of that said 3/4 hp or better.