RE: Class sizes
Giant scale usually refers to scale airplanes with wingspans 85-90 inches (and greater). Haven't really heard the terms 'large' scale and 'regular' scale used very often, but I would think that most people would consider 'regular' airplanes ones in 45-55 inch wingspan range (.40-.46 size engines), and consider 'large' airplanes ones with wingspans in the 60-75 inch wingspan range (.60-.90 size engines).
As far as electrics ...., with the advances in batteries and motors in the past few years, electric airplanes can now be as big as any glow/gas airplane. However, you do not see many electric large or giant scale 'scale' airplanes. One of the reasons for this is the lack of engine sound. Most people that build giant scale airplanes (especially warbirds) want to hear the sound of a combustion engine. Bob