If you can afford a bigger model then there is no reason to avoid it. Bigger planes usually fly better than smaller ones and are easy to track. Tuning a gas engine is quite different than a glow engine and mishaps are costly. There is a great big plane called Telemaster which can be powered with a gas engine and I consider it a good first gas plane, it also does fly like a trainer and does mild aerobatic maneuvers. Be aware that Gas Fuel is very different to handle than glow fuel, so too much care should be taking. As I mentioned, is also a big difference on tuning a gas engine than a glow engine, but once that you learn it, you will find it easier to handle than a glow engine.
Good luck!!