According to the schematic posted by Loudthud a few years back, the Alpha outputs are wired in parallel; just like pretty much every other
amp on the planet.http://sunnforum.ampage.org/index.php?topic=7152.0
You can wire any number or configuration of speakers you want just don't drop under
4 ohms impedance, higher impedance is fine as far as keeping the amp happy but you will diminish the amps output, and stress/heat, as the impedance increases.
The wattage rating of the speakers have no influence on the amps performance or longevity, but generally speaking the higher the rated watts are on a speaker the less efficient (sensitivity) the speaker is, and a lower sensitivity speaker will make less SPL than a higher sensitivity speaker will with the same amp.
TS connectors, and the lower the gauge the better; gauge gets more important as the length of the cable increases. That said, with standard connectors gauges under 12-14 can be tough to work with.