I'll second everything n7tb said. And add a few things... Lots of guys use aftre run oil (and transmission fluid IS a good one) and lots of guys don't. I don't use it except for long winter storage.

There are lots of good engines out there. The 2 that were mentioned are very good indeed. If you can aford the OS get it, but if money is tight, The Thunder Tiger will do fine. Whichever brand you get, what you should be aware of is "Bushings vs. Ball Bearings"

An Engine with bushings will be cheaper than an engine with ball bearings, but an engine with ball bearings is considerably better. You can usually tell which is which by looking at the very front of the engine casing (right behind the prop). A Ball bearing engine has a housing for the bearing which makes the casing much thicker than a bushed engine.