"How does one know the light cycles needed for plants at different stages for the artificial lighting?"

ANSWER: In nature, plants are able to recognize the length of time, probably even down to the minute, of sunlight in a day to gauge whether they should be growing their stems, leaves, and roots vigorously, or, when temperatures and other conditions such as nutrients permit, begin to produce abundant blooms and fruits.

Now, in order to recreate this change in duration of light being emitted at your plants, you must know the magic number. Yes, there is a magic number under which all plants (whether they bloom with more than, or less than this magic number) obey. If one changes the amount of light a plant receives from 24 hours, being on all day, down to a smaller amount such as 18 hours, not much will happen! You have not gotten down to the magic number yet. What is important to know, is that no matter how close you get to this magic number, things don't start doing much till you actually reach it.

It just so happens that when plants begin receiving 12, or some say 13, hours of light, and 12 or 11 hours of darkness, they are forced into what is called their flowering state. As previously stated, the plants will redirect their "hormones" and growth factors in a way such that the growth is now focusing on growing buds and blooms, and ultimately, tasty morsels for us to eat! And this all happens, again, at 12 hours of light per day!

"What's the cheapest diy way to set up hydro/aero systems?"

ANSWER: I prefer to use what is called the DWC, or Deep Water Culture type of setup because it is very easy to understand how it works, and is very economical. As to how I make them, that is very easy. If you don't mind some reading, reading from a MJ forum I might add, I have included a link to some invaluable instructions about how to create a DWC bucket:

"Are there better systems for different types of plants?"

ANSWER: Yes and no. I think it all really boils down to how much root space a plant needs. Obviously, a banana tree will be different than a rosemary bush, in many respects, but root space will determine which system would be more suited for the plant. I have no list of optimum systems for every plant out there, so I won't be of as much help here. Many people around this forum should be able to answer this question though.

Here is a link that might be useful: DIY DWC Bucket

ALSO:

I forgot to mention that you can use the same amount of artificial lighting from seedling, through the vegetative stage. Only for flowering does one really need to change the light cycle. You can use 24 hour or a full day of lighting on the plants until blooming, but for economical reasons, you may choose to do 18 hours of artificial light.