1. You can buy a high quality STJW 12-3 25' cord and cut off the length you need. You'll also need a strain relief connector, usually 1/2" male pipe threads, like this:
Sigma Electric 49212 1/2-Inch Strain Relief Cord Connector, 1-Pack

2. You can do what you like. The issue is matching flow, filter, & piping. Most IG pumps generate more flow than most AG filters can handle. Overpowering a filter EITHER damages the filter OR results in poor filtration, as dirt is forced through the filter.

3. Standard 1 and 2 speed IG pumps have been left outdoors for years, with good results so long as the pump is kept off the ground and not covered with debris resulting in overheating.

The feedback I've seen here on VS pumps suggests that they are MUCH less reliable than 'old-school' pumps . . . and when they do need repair, the repairs cost nearly as much as a new pump. Also, the savings, compared to a well-selected 2 speed are small. So . . .
+ I do not recommend VS pumps in areas subject to lightning. Lose the electronics and you have lost the pump. Lightning is killing a LOT of these pumps.
+ If you can use a standard 2 speed efficiently, the result will be nearly as economical month-to-month, cheaper and much more reliable.
+ In many cases, an existing single speed can be upgraded with a new 2-speed motor.