Typically Saitos do break in rather rough however I do not belive that an isolation mount is necessary. I didnt use one on my 100 and it was fine. Just run it in per mfg recomendations 40 mins of break in time approx 3 to 4 tanks. I have never put a twist together so I cannot help with the battery placement and fuel tank size questions. But I would say that its a fine 3D trainner. Quick build prob easy repair. And you can tune it down so its not so wild at first. I will advise this, if you have never flown a 3D plane I would not recomend putting the CG anywhere but right on or slightly nose heavy at first these planes can get very touchy when they are tail heavy. If you have triple rate buttons on your remote or even duel rates I would use them and have a nice low rate to start.