Looking at the ripmax website who distribute the Wot trainer , the recommended motor is a KMS Quantum 4120/05. This is available from BRC hobbies here. It is a 1200 watt brushless outrunner. The all up weight of a Wot trainer should be 5.7lbs, giving 210 watts per lb. This is a bit OTT for a trainer and it could be calmed down with an 800 watt motor giving 140 watts per lb. incase you didn't know, anything will fly on 100 watts per lb. however, the smaller motor may move  your centre of gravity too far rearwards requiring lead in the nose.

On the subject of whether electric power is better for a beginner and/or trainer there are many pros and cons. electrickery sounds simple, but requires some knowledge to execute well (although that's where Timbo comes in handy) However, electric power is clean and reliable when a setup is found that works. I trained on an IC trainer and cannot fault it. If you get an OS or Irvine engine you will not have any problems, they are so reliable.  Costwise, there is nothing between them now.

2.4 ghz is also a good move if you haven't already purchased radio gear

Jonathan 

"Some may think this is an odd comment from me, but as a first trainer I also suggest IC rather than Electric".

That is very odd indeed, but good advice Tim