First of all, nice setup! I like it.
If the tank has been running for three months, then it's already cycled. With no bioload (livestock) up until this point, the plants are consuming any ammonia as fast as it's being produced... which explains why the tests are 0-0-0. I wouldn't worry about the livestock at this point, only the plants. I'd recommend that you start dosing the Flourish right away, along with Flourish Nitrogen. Start with the minimum recommended dosage, and gradually increase as the plants grow and fill in. At the same time, you could also gradually increase the lighting period to 8-10 hours/day.
I agree w/ Ddrizzle that it's easier not to get algae w/ CO2, which is why it's important to gradually increase ferts and lighting. If you do too much too fast, you're likely to get an algae bloom.