Hello and welcome .
I’d say (expletive deleted) your neighbors for starters . They are going to hate you anyway ; so don’t worry about that .
I see opportunity here . Trust me 😁 ; a garage can become a house . I’d certainly go for change of use . Forget any rules for changing back . At a later date you then have an established footprint for a dwelling.
Don’t concede to get what you want at the prospect of future opportunities! . Slowly , slowly , creepy monkey ….
A future independent house is the prize here …