I like the idea, I got to wave ten before dying. I would have loved to be the one moving the character as well as the flashlight. It would be cool to be moving through a space to make it more dynamic and interesting and you have to survive a set number of waves before moving into the next 'area' and getting the chance to buy the upgrades you mentioned.
You can already buy the upgrades, if you click the shop button. Unless that doesn't work... if so, lmk. The idea was to have it fit the theme of "You are the Weapon" by ONLY being able to control the "weapon" (in this case the flash light) I have thought about having the girl, instead of move randomly, move on a set path or something. Perhaps she could walk through different areas like you said, I will experiment with this.