If you are looking at changing forks, and it's for a commuter, dump the suspension, and get rigid. No point with suspension for use on the road, and rigid will work fine off rod.

For your questions

1 - Why spend more money? function over form.

2 - 20mm! most 100mm forks can be shortened to 80mm using an internal spacer, could you do this rather than paying for a new fork?

3 - Forget suspension correction, this was/is an issue for 26" bikes which were designed for 40-60mm travel forks, the Karakoram 2.0 was only available for MY2011, and as a 29er, so a non-existent issue.

For the Orange F7 fork, being a 26" this will throw the bike's geometry off, if you can even get the wheel to fit. Would look for a rigid fork, plenty of options at multiple budgets out there.