I agree with Mahgister.
The room is definitely the weakest part of the system, if you want to call it a part,
Not only is the room a part of the system, it’s the biggest player in the system. Your room will affect the sound of your system more than any single component. Also remember, carpeting, furniture, furnishings, room shape, etc. are all a part of the acoustical profile. Some good, some bad.
Acoustics in my opinion are challenging and I wouldn’t hesitate to consult with an expert or two that work in the field. Also remember, you don’t have to make all the changes, just make the ones that your circumstances allow. Another thing to keep in mind is that some acoustical issues can be addressed electronically much more economically.
As far as upgrading your actual components, if your plan is to upgrade your entire system over time, I would upgrade the components that you think will change the least in that time frame first and the ones that could change the most, last.