I'd say there's not a lot you can do with the garage, overall height limits and ceiling height to garage perhaps? Limited info and unfamiliar with site, etc. so just really guessing here. The stairs however could be changed as could the balcony, etc. Can't see issues here why it can't be amended to suit your requirements. You never mentioned the issues with the designer but perhaps stay with them as redesigning through another may not be ideal either! Some won't touch another designer's work and will start from scratch. Give them another chance to explain why it is all done this way. Allow them the opportunity to amend it and depending on your council, use a SECTION 96 if possible. Council will soon let you know if they can accept it. Remember they've been submitted so I'd have to presume you were happy with them beforehand. Clients changing their mind or have difficulty making decisions happens regularly as its all quite new to them. I too have had clients that love the plan's, get submitted then decide that want to change something that has been there from the beginning.... Windows and doors are usually what my clients change. Frustrating for client and equally if not more so for the designer as it affects the whole plan set and documentation in many cases. I do know many designers will railroad their clients into decisions based on their own visions but this is never a good thing. It's a collaboration between client, designer, council, engineer, builder, etc. and sometimes a bit of compromise by all parties.

best decision would be to incorporate any changes for the entry with the upstairs renovation .please post photo of the new upstairs and roof and what do you plan for the front yard, fence and driveway?

Though I don't know for certain, I think the cotton/linen shades are removable. I wasn't able to determine this by my searches. This could easily be confirmed by making an enquiry to supplier before purchase. Alternatively, a handmade one could be made removable by making shade slightly larger than frame and making ties.

Measure all your furniture and make actual size templates with pieces of paper. Then move the templates around the rooms and see what works best. This is a lot easier that lifting and moving furniture. If you want the dining in the lounge because that works for you then do that. Don’t be dictated to what a room is used for because that is the name of it on a plan.