In theory, there's no limit to the size of wavelength, but ...?

Theres no theoretical upper limit on the wavelenght of the EM-spectrum. On the horizon of our visible universe theres an barrier of "infinite redshift". Also, EM-radiation radiated by a body falling into a black hole will also redshift into "infinity" at the event horizon.

there probably is a limit, related to energy. if i recall correctly a photon contains the energy of an electron falling to a lower orbit. at some point, is there an energy level lower than is available from any orbit to any other orbit? oh my, this is going to get beyond me. obviously it requires far more physics than i've studied. eg, with only discrete levels available, how is it that all light and radio, etc levels are available for use? sorry, this is as long as i can hold my breath. maybe we'll get lucky and someone smarter than me will consider the question. i'd be really interested in a better description. Edit: "half the size of the universe." i like it, i like it. :-) but i don't see an explanation of why the photon energy level spectrum is a continuous curve, rather than consisting of discrete steps, defined by energy levels available to electrons falling from one energy level to a lower level. why are there not "stairs"?

It is wrong to refer to the speed of light as a speed limit, it sounds like light can travel at any speed up to that limit. It does not, its speed is always 3x10^8m/sec. All light travels at this speed. Electromagnetic radiation is a full spectrum with wavelengths that stretch from subatomic distances of about 5x10^-14 metres for cosmic rays through 4x10^-7 to 7x10^-7 for visible light and on to wavelengths of kilometres for radio waves. There are no limits in either direction, electromagnetic waves are defined by their fundamental properties and mode of generation. There is no search for new extremes.