[chumbucket]

Well, if I'm not mistaken, the V20 will handle up to a maximum of 235 HP. Yes, you need a 25" shaft length. There are some motors that are made as counter rotating. This is a term that is used with dual engine setups where the two motors will be turning in opposite directions at the prop. This gives the operator greater control of the steering torque and handling of the boat. Counter rotating engines didn't really come around strong until the late '80's-early '90's when big twin engine outboards became popular. Generally, if someone is selling a single engine, you can bet that it is of standard rotation. Counter rotating engines are usually sold in pairs and advertised that way.
Getting back to the HP question. Do you need 235 HP? no. Might be a lot of fun, but it would be very thirsty on the fuel consumption. On the low end, I wouldn't go much less than a 130 - 140 HP. My buddy's V20 has a 115 Merc and it feels very much under powered to me. I've got a V20 Center Console and run a Yamaha 150 on it and I'm very pleased with the performance as well as fuel consumption. I don't have any real hard numbers yet for the consumption, but can tell you that with the 150 I max out at around 38mph and typically run at 25 - 30 mph cruise speed. At cruise speed it seems to be very efficient.
There are things you can do to help the lower power situation as well such as trim tabs, shifting weight in the boat, reducing weight, etc. Hope this helps.