As always, it all comes down to money

Anything (within regulation) is possible, with enough money. Money is the ultimate controller when it comes to these sorts of decisions. We deal with this type of question on a daily basis, and manage it professionally via a Feasibility stage of service that helps clarify and explore scenario options properly. To get accurate answers to your questions you need a design professional (ie Architect or experienced Building Designer) on board who understands renovation scenarios and construction costs to help clarify your options. You won't get accurate answers for free on a forum, but hopefully your post will help direct you appropriately.

Off the cuff, if you budget is anything under $400-500K then something like previously drawn ( upper level extension in conjunction with renovating extensively downstairs ) practically is going to be likely end up proven beyond budget, regardless of layout or the minutia detail of extra bathrooms or whatever.

Begin with defining your living requirements together with a nominated budget. This sets your "brief". You then need to explore whether your brief is appropriately aligned in terms of scope and budget, and work through what your options are.

No don't talk to a builder as a first port of call about this sort of thing, generally don't talk to a builder about design decisions.... they build, design is not their area of expertise......design and construction are two completely different areas, although related, but design precedes construction .......builders have a critical role, but at the back end of the process...

Hope this helps guide you a bit

Good luck & stay safe.. PD :)

www.pauldistefanodesign.com