I would start with architect or look for design/build contractor in your area.

Invest in an architect.

Yes you should look for an architect first. They will be able to recommend a good contractor and even an interior designer if needed.

They can also do a "Master Plan" for you of everything that you want to do in the future, but aren't ready to do now. They can help you determine the best game plan for phasing the remodeling since you don't want to do it all at once.

Also, if possible, it's always helpful to get the contractor on board during the design phase too because they can work with you and your architect in deciding the best methods of approaching the construction phasing.

Interview at least three highly recommended architects. Ask them to give you a tour of a project or two. Call their references and ask if they would hire the same firm if they could do it all over again........

Hire the firm that you feel most comfortable with.....and have fun.......

It sounds like you need an architect for sure if you are going to do an addition at some point. You may consider hiring an architect that has an interior designer that they like to partner with to help with the finishes, furnishings and decor. Eventually you will need to hire a contractor to do the work as well. Honestly, you need all three! If I were you I would look for an architect/interior design team to start you out on the right foot. They can help you design and budget for the different phases as well as recommend a good contractor to build it when needed. Houzz is a great resource for finding these professionals as well!

I would recommend getting an architect as well...but see if you have one who is also a contractor. While I used a separate contractor for most of the work on our whole house remodel, it was invaluable to have an architect who knew the relative costs of making his "vision" for each space come true. Definitely helped us to tame some of the initial suggestions.