The warranty is not void if you disassemble the pump.
No, an 115V motor is needed to run on 115V power.
These pumps are capable of pumping fresh water, sea water, and salt water.
The holes should have freeze plugs in them, and all LC pumps leave March with these freeze plugs installed. If they are missing, it is because the pump was not winterized properly or they were blown out from compressed air. Individual freeze plugs or new rear housing should be purchased.
The pump can be mounted horizontally or vertically. If vertically, have the motor end below the pump end to prevent air lock. For the AC pumps, the outlet can be rotated in any direction except pointing downward