In practice this is rarely achieved. However, as beacons are fixed in frequency they can be listened for carefully, and even if not fully readable, QRP beacon signals may still provide valuable indication of the presence of openings. Power levels of 5 to 10 watts are most frequently used and provide perfectly acceptable signals. Even milliwatt transmissions can be useful, though these are easily overlooked. Power levels will probably be dictated by design considerations, but obviously the more output power the wider the beacon coverage geographically and the more reliable the reception.
Frequency modulated transmissions have some technical advantages but take up spectrum space.
Because of this, amplitude modulated signals may be better. Although there is no reason that speech or data transmissions could not be used in a beacon, CW is preferred for bandwidth and because it is easily received. But CW speed is a tricky one. I guess 15 to 20 wpm is OK as everything gets repeated and there is always another chance to copy for those who find cw difficult. Antennas should be omni-directional unless the beacon is to test propagation on specific circuits.