RE: take off/landing on grass???
Many RTF planes have landing gear, but they're just for show. Most of 'em have pretty dinky wheels, and no true rudder control for steering on the ground. They require a smooth dirt/paved runway pointing straight into the wind, and a bit of luck for ROG and LOW (Rise Off Ground, Land On Wheels).
You need to step up into more "serious" planes to get true ROG capability, and nearly all of those require some assembly. Most GWS stuff, for example, will take off from smooth grass. I know for a fact that the E-Starter does well, even in fairly tall grass. Note that this isn't building, it's assembly. The truly tedious tasks like stick-building and covering are unnecessary, because the plane is made of foam.