Hello Hope. Very exciting news. I'm a consulting engineer at Kohler Ronan (we design all the active the building systems that maintain and protect collections and building overall) with 17 years of museum projects experience, and have been fortunate in my career to collaborate with several architects and planners. Happy to see Guy of Museum Insights recommended by a few others here. He's very straight forward and would help you get the project pointed, recently completing the Art Complex with him. I'd also recommend Erin and Bruce at Cooper Robertson, an Architecture and Planning firm with several museum projects ranging all sorts of sizes. If it so happens your project needs are substantial, their firm has the bandwidth to go right into design, and are great collaborators if you would like to bring another architect into the design phase and maintain Cooper Robertson as your Master Architect to ensure all program and museum planning goals are achieved throughout the entire design process.
If your project has landmarked/historic registered buildings, you also may want to take a look at Beyer Blinder Belle (whom we often work with at the Metropolitan Museum of Art), and John G Waite Associates which we worked with at Steamtown (National Historic Site Train Museum) in Pennsylvania.
I would also recommend you and potentially your museum director attend the Mid-Atlantic Association of Museums - Building Museums Symposium. This is effectively the best place to learn about several other museum projects from museum owners/operators and construction departments, and meet other museum professionals, architects, and engineers like me that plan, design and execute museum projects. https://midatlanticmuseums.org/building-museums/ . The next one is in Philadelphia on March 6-8.
There are a lot of other firms i could recommend as well, however it really comes down to what your needs are and selecting a consultant that listens and asks the right questions to ensure your needs are met. Attending the MAAM Building Museums Symposium is hands down the best way to figure out who speaks your language so you can narrow down your choices to decide who you want to onboard and when, and what you need internally to make sure your institution is prepared for the process.