RE: First time speeder needs help
Either the Viper or Predator would be fine. I really don't see a huge difference between the two. The viper does come with a backplate mount, although not perfect works ok. Both require a few basic mods which have been detailed in this forum. Make sure you check up on them before flying.
The .46fx is perfect, we use that motor on these planes for our local racing rules. Were not using pipes, so I'm not sure what the fastest prop will be with that config, but were getting speeds between 120-130 mph with the standard muffler.
I don't know that JR servo, but I do know that people are running standard BB servos in these planes.
You do not have to have a bladder tank, but they do help. If you don't use one, just make sure its cushioned well, and you should be fine. I would suggest not running out of fuel in flight if you don't use one, as your engine will go lean near the bottom of the tank. Placement of the tank is not as critical for a sport plane. We flew these types of racers for years with the tank up in the nose and never had a problem. I notice a very small improvement with the tank on the C.G.
Have fun. There are plenty of threads on the two planes you mentioned so do a couple searches, and I'm sure you will find plenty of reading