3 week vacation - prep plan?

[corpusse]

Your plan is good, but I'd test out the friend on scraping the glass and if you don't think they can handle it just have them clean enough in the middle to see in.

I don't think you should be concerned about the lack of water change for 23 days unless the primary reason for the water changes is nutrient removal.

I take it you don't dose and water changes are how you maintain your alk / calcium? How much consumption do you normally have? That would be my only concern but if its a lightly stocked tank you are probably fine.