No, its not bad to have tinfoil or any other reflective surface on the walls. just vent all the warm air out. Its not enough just to put a fan in if the system is closed, there needs to be fresh cool air all the time. get a blower fan and pump the air outside if you can, then cut a hole for intake in the door or wall and put a vent filter over it to keep bugs out. you can spray at the end of the light period, but be wary of getting the flowers wet when they start getting dense. youll get some yield off these plants but youd get a lot more if they were bigger (bushier) when you started flowering. it looks like they were veged under an incandescent bulb. PS- hang your thermometer at the same level as your growth tips and right in the middle under your light to get a better idea of the direct sunlight that your plants are experiencing.. 75- 80F for day, and 10- 15 degrees cooler at night. 40- 50 percent humidity for flowering. you can get a humidity gauge at the pet store for 5 bux. good luck!