lawn mower engines are vertical shaft. you will need to modify it for horizontal output.
it will go as fast as you gear it. if you gear it for torque it will accelerate faster but have a lower top speed. and if you gear it for speed. it will go fast but it will take a long time to accelerate
If you have an edger with a B&S engine, that'd be fine. You can find them anywhere. $30 on eBay, shipped. Usually you just need to clean the carburetor, adjust the coil/points, and you're off.