If you use enough wire nuts, you can wire a lot of things off one amp. Should you? That depends.
If the music you play is hours on end of continuous sine waves, then the "rms" number is what you want to allow for in your amp calculations. If what you play is actually music, the program number is a good starting point, with headroom being a good thing if you know your system and its limitations.
On many amps, the power sweet spot is 4 ohms per side, so an amp with a 4-ohm capability of 1600 watts per side would be a good fit for 4 subs - two per channel.
There are many variations on the theme - if you like to run things hot, you may be able to bridge your amp into a 4-ohm load (either 2 subs if your amp is small, or a series-parallel combination of 8 subs if your amp is enormous), but this is harder on the amp, and potentially harder on wall current.
If it were me, I would get amps large enough to run in 2-channel mode, each side powering 2 subs at or above the program rating.