ported box

A long, thin port is less accurate than a more square design and has greater air turbulence.  Keep any port design at a 8:1 ratio or more square.  One inch is too narrow to use.  One and a half inches on the short width would be the narrowest I would design with.

3 X 4 is 12.  1 X 7 is 7.  These don't compare, but if you were just throwing out numbers to qualify what "more square" means then you are right that the 3 X 4 is better.

Use a rubber grommet for the wire through the box if you are concerned about chemical interaction.  For myself, I haven't heard any stories of wire insulation being damaged by resin.  And if the wire, in whatever way it's secured through the box, is secured completely, there won't be movement of the wire inside the box when the outside part of the wire moves.  But if there is some movement, no harm done.

For your question of ported box designs, the easiest way to build a slot port is to use the effective inside width of the box for port opening length.  It keeps the construction at its simplest for both the design and the building of it.  Some premade boxes have poorly designed slots, so don't put much into those designs, but many are correctly built.  If a slot opening is 12"  on the long side and you want to maintain an 8:1 ratio at a minimum, then the width of the slot should be no less than 1.5".  Then, if you wanted to lengthen the port for better tuning accuracy, you could widen the slot design to say, 2", and work the port length out again using that larger square inch opening.