Sounds like a great idea! If it were me though, I'd want a high-ceiling bus unless everyone in your band is under 6 feet tall. You will also have to do something about sound dampening especially the metal ceiling. Also, the space will feel small pretty quick once you get everyone plus their equipment in there. I love the size of my 8-window bus. More space than a "shortie" but more maneuverable than a full-size bus. It takes up exactly two parking spots if I "pull through" and 5 spots if I parallel park.
Jump in! 5K in the scheme of things over a lifetime isn't much--you'll spend more than that on the patio cover on the house you will have some day Do plan what you intend to do with the bus, research it and develop plans B through Z---but go for it!