This was a delight to read! I like how you've sort of flipped canon in some respects -- e.g., in canon Harry lives an altogether too exciting life, and Snape is source of worry, a nuisance among many; but here Snape is the sharp edge in Harry's complacent, smooth life -- but maintained/incorporated other aspects, including general characterisation.
Also, great banter, a Ron who made me grin, and who could forget Smithers?! Excellent job. :)