That fork won't fit your bike.

As others have mentioned, you need a 700c/29er fork, a fork for a 26" bike will be too small for the diameter of the wheel, and the rim / tire will hit the forks brace.

For the travel, not seeing that as too much of an issue, as a lot of that should be taken up by sag, but the Rock Shox you have ordered is a very budget fork, and may not give the option for this, it will change the steering slightly though. Can't see that it is an upgrade, more realistically, it's at the same level as a stock fork, or a downgrade.