How to write a letter to nominate an awesome Professor for an award?
First, thank you for wanting to do this! Once the awardees have been announced, no matter the result do let your professor know you did this, and pass on the award packet you created (let any letter-of-support writers know you plan to do this, as a courtesy; they probably won't be fussed about it). Your respect will mean more to your professor than the award!

Now, to your actual questions.

Pointers to mention. Think of this like a cover letter for a job application. You want to address as many of the listed criteria as possible as specifically as possible. (Award-ceremony emcees often quote from nomination letters, so try for good soundbites!) You don't have to hit every single one (especially as that list is rather long), but try to touch on half to three-quarters of them.

Length. Often the award criteria will specify this. If not... honestly, I'd call or email somebody in the office sponsoring the award and ask what's typical. I've seen one page up through almost ten, and it's not good to err in either the too-short or the too-long direction.

Tone. Err on the serious side. If you have an anecdote displaying your prof's sense of humor, use it if it speaks to one of the award criteria ("quality interactions outside the classroom" or "classroom effectiveness" might fit), but be absolutely sure the humor is one hundred percent harmless first -- you don't want to land your prof in hot water, you want them to win the award!

Good luck to you and your prof!