To try to answer your questions, all engines will work perfectly well using just methanol and oil. Nitro has the added benefit of allowing the engine to produce more power although at the expense of higher fuel consumption. It also makes tuning easier because it gives a larger range of adjustment where the engine will run satisfactorily. In some cases it can make the engine easier to start although that shouldn't be a problem if using an electric starter. Virtually all engines can handle up to around 15-20% nitro but more than that and you could start running into problems such as blowing plugs regularly. For sport flying it's best to use the minimum amount of nitro you feel happy with. In other words, the engine starts easily, idles well and has adequate power for the model to do all you want.

As far as brands of fuel go, and I base this on reading their specifications because I make my own fuel, there are some that seem to be good and others I wouldn't touch with a barge pole . The major difference is oil content (and type of oil). IMO a fuel that's labelled as having at least 20% oil with a good content of that being castor is a fuel I'd consider using.