Your isometric art looks really good! Todd Barchok is currently in the process of redoing the code for IsoTower from the ground up. According to facebook, most of the functionality is there but the game is all text (with rooms and agents represented as boxes with differently-colored text. When I contacted him several months ago, he was open to custom content (including new rooms and art replacement) but told me that IsoTower was not ready for mods at the time. I recommend you keep making art for fun so that you can mod the heck out of IsoTower!
Project Highrise has its own distinct art style and is designed for only 1 layer of rooms in a classic (SimTower style) cutaway front viewpoint. The more I learn about Project Highrise, the more I like it and the less I desire to mod it (since it seems like the base game will add most of what I was originally planning on modding in). IsoTower seems more like the project better suited for modding in your art. If you only want to make art without doing coding, I will gladly help.
Personally, my first priority is my coursework for Uni and my free time during breaks will be spent reconnecting with family, studying, modding Civilization Beyond Earth, redoing all my OcramTower art (I made a graphics pack with double resolution images of all 1-3 star rooms & transport and full color sprites for the agents, with new variations) in InkScape (possibly with top-down and isometric views added), and peaking through CityBound's modules in GitHub (for eventual modding of the upcoming Alpha).