I am certainly not an expert on engines so consider this post worth the price I charged for it :-)
Once I got my first 4 stroke I quickly gave up the two stroke engines, never had issue with the two strokes, just like the 4 strokes better.
All of the engines I am currently running are OS and Magnum 4 strokes.
As a general rule of thumb when you select your prop you will need to choose one that will load your engine between 9000 to 10000 RPM sustained on the ground, a little more than 10k is ok but I would not load it below 9k.
You will need to set the needle valve / RPM with a tachometer (I am sure there are people out there that can do four strokes by ear but I would not recommend it to start off with). While the GloBee tach has has its share of criticism I have had one going on 3 years and it works great.
Don't adjust anything other than the needle valve unless there is a very good reason to do it.
My experience has been that the four strokes have required no more maintenance than the two strokes.
Don't mess with them and they will run fine for a prolonged period of time.
I recently switched from 10% nitro to 15% fuel (just because I got a good deal on it) and I got aa average of 500 RPM increase on my OS engines and 900 RPM increase on the Magnums. I did not expect this much difference but needless to say I would now recommend the 15% nitro.
There are props that say they are 4 stroke props, I have some of them and I like them fine, right now all of my planes have either APC or Master Airscrew Scimitar props on them (just because I like the way they look). Bottom line any prop for a glow fuel engine will work.
What size prop to run ?? Well I don't know what to recommend for the 48 Surpass but the RPMs listed below for the various engines were all measured in the last two weeks. I live near Dallas so the temp was 100+ and humidity was between 40 and 60%.
15% nitro, 20% oil, sustained RPM on the ground:
OS 91 APC 14x6 9600 rpm
Mag91 APC 14x6 10200 rpm
Mag 70 MAS 13x6 10000 rpm
OS 70 MAS 13x6 9700 rpm
Mag 61 MAS 12x6 10200 rpm

I would guess 11x6 would be a good starting point.

Oh a couple more things, I would run the engine right side up on the test stand before mounting it upside down in a plane, it will just be easier to fiddle with that way. Forget the choke and use an electric starter, again its just easier.

Hope you have fun with it.