That's one way to go, usually don't have enough heating capacity because they are 115 volt. Mini splits will need 220v so you have to add in electrical costs. If you don't like looking out the window and having to loose the space in front of it, you can go that route.
The mini splits are the way to go. Most schools today use them instead of ducted rooftop systems and many commercial applications as well. Some brands offer the adaptability of multiple indoor units with one outdoor unit. For maximum comfort and utility savings I would go with that. Thirty five...