Smaller units will require a smaller backup genset to run one at a time if you want to do that. (Inverter units are already very good with gensets, btw.) As others have pointed out, efficiency may be higher with the 1:1 systems. Some mini splits can cool and heat simultaneously transferring heat from one room to another, but these are rarely seen in residential situations because they are more expensive. It may only be available in systems with more indoor units. There is one downside to heat/cool units if you only need cooling. Complexity is increased meaning more things to break. I don't know if that is significant. I had a reversal valve fail under warranty which cost the installer, but not me. Note that if you have oil heat, the heat pumps may be a less expensive way to heat. Two 1:1 systems means another compressor unit sitting outside. If I had all 1:1 systems, I'd have seven compressors sitting on pads :-( You should know that the better mini splits have inverter-controlled compressors and variable speed blowers. This combination increases efficiency and comfort by stabilizing temperature and improving humidity control. Now consider this. A single unit that can throttle back to 30% of 6000 BTU can run at a 2000 BTU minimum. If you have an outdoor unit that can run 12,000 BTU your minimum becomes 4000 BTU. I believe that the smallest multi Mitsubishi compressor unit is 20,000 BTU so in this example, its minimum might be 6,000 BTU so you gain little from variable speed unless you are running both units at the same time. This would be enough to make me go with 1:1 in your situation despite "slight" increased cost and another unit to maintain. In addition to those arguments, if the price is similar, but you are running one compressor at a time most of the time, you get more longevity for the compressors.

Most run to 0*F - especially heat pumps, which you would want. Installed (4) zone Samsung at my Mother's Home in Lindenhurst...works like a charm. Go skiing out West (Colorado) , you'll see them all over the place there as well.

How much extra are you being quoted? Right off the cuff I'd say I would go for the heat aspect as it would give you greater control over marginal heating needs and spring and fall, and might need some heat in the early morning or late evening, but cooling during the day.

OP, if you are still reading this, and manage to get the existing drain unplugged, I have some suggestions to keep it from clogging up again if you want to keep trying to use the existing drain to avoid tearing into your walls. Please note two things, however, if you can get to the other end of the pipe or tube in your walls, you stand a good chance of unplugging it. Also note that fixing and painting drywall is a relatively inexpensive process that might allow a more permanent fix by changing to hard pipe or a different flexible tubing type. Make sure that your unit has its drain running out to the same side that the opening in the wall is on. Most of them have the option of draining out either the right or left side, but I have seen them installed such that the condensate runs to one side of the appliance only to have the pigtail drainage tube pass all the way across the back to drain out the hole on the opposite side. Make sure the pigtail has as even a downward slope from the condensate tray into the wall as possible. There should be no upward slope anywhere because it will encourage water and crud accumulation. It should be fairly easy to remove the condensate tray completely for cleaning. (I feel like you are already mostly there if not past that point if you have removed the drain pigtail. Check YouTube for videos.) Use some condensate drain tablets to discourage microbial growth in the tray and the drain lines. Now they are marketing specific products for mini splits rather than having to cut down gel tab and whatnot products designed for larger ducted systems. Rectorseal ACTABS DMSS is one product and PurCool Green Mini Strips are another. Note that if you take the main cover off and remove the condensate tray you will probably have great access to the entire squirrel cage blower to clean that with a vacuum cleaner and great access to the coils that can then be cleaned with a foam cleaner if visible lint is caught on that. If no visible lint is in the coils, you can spray on a neutral to slightly alkaline pH coil cleaner like Nu Calgon Evap Pow’r -C. If you keep the crud out of the coils and blower tube, it will probably help keep the condensate drain system more clear and condensate flowing.