can mono push 2 subs or 1? It can push 1 to what ever amount of subs you connect to it. Multichannel amps are made for full range, mono block was made for subs. Just because an amp has only 1 channel and you want 2 subs doesn't mean you need a multichannel amp, unless you want to try and filter out every last bit of highs going into the amp. Monoblock, you will not have to filter out the highs, since the amp will not register them at all, best amp for subs, hands down. Remember, mono=subs, multichannel=full range.
As long as you match the OHM load that you plan on running with these subs and the RMS wattage you will be fine. You can wire the subs to a 1 OHM load or a 2 OHM load, and the amp will need to a total of 900 watts RMS, or 1800 peak. Never look into peak wattage, it means absolutely nothing unless your in marketing.