Nothing like the sound of a good 4 stroke. Yes, they have more moving parts and are more expensive than 2 stokes. But once broken in and set up properly they just run forever.

I would suggest you stick with either OS or Saito for a first attempt. They are user friendly and very good quality. The lower priced engines just don't stand up as well in my opinion (and I've flown 4 strokes for 25 years). I know there are others who disagree. YS's are great, high performance, sophistcated machines and they have many fans. But these folks tend to have lots of experience with them.

As someone mentioned, 15% nitro is fine.
Use an OS #F glowplug regardless of what brand 4 stroke you decide on
Follow the manufacturer's instructions for break-in and tuning. They know a lot more than the folks using them.
Use (at least) the recommended oil content. I like to have some castor oil as part of my total oil (2 or 3%)
For your first engine, get a tach and use it until you get used to the sound. Stay in the recommended rpm range and prop size.
Check the valves after break-in and then maybe twice a year or if it ever seems to lose power.
Run the engine 'dry' after every flying session. Use after run oil if you live in a location with high humidity or use it for float flying.

I will now get a lot of feedback on the above, a lot of it negative. I don't care - the above works for me, and will work for you as well.