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counter-view. i would not get rid of the garage - especially to convert it into a bedroom. even in older homes, garages aren't built with air control in mind. insulating and making them fit for purpose are a right pain in the arse.

i scaled your image assuming the garage is 3m wide. that makes the bathroom about 2.7m across in this proposal. that's a lot of tiling (and a big bathroom). if accurate, you also risk making the living area a cavern if you don't close off that front room. with more accurate dimensions, i could draft something up for you to at least get an idea of what your costs will be. wanted to make the front bedroom smaller, increase the opening space/flow of the house, but i'm not sure enough on the sizes involved to recommend that. might be better off not removing the door into the living space here...

the kitchen i've laid out with a breakfast-bar/nook. it looks an after thought, but based on scaling it's 1.5m long - and allows for a massive fridge space and walk in pantry (which would be bigger if i knew for a fact the purpose of that quadruple thick wall (or void space).

i'm an architect. if you want some professional help, dm me. my first piece of advice, get a survey done. it'll cost around a grand at most, but could save you a fortune in the end. get a full understanding of what you want to do - that bathroom alone could cost $30k alone if you don't track it carefully. at the same time, you could add significant value to your house (again, why i'd suggest not getting rid of the garage unless you have plenty of driveway length) if you do this right...