I am glad that you know a lot of the basics in fish keeping.
I am unfamiliar with Seachem's bacteria seeding product. If it is just a re-branded product from Dr. Tim's, then it is basically the same thing as Tetra SafeStart.
The thing with changing water hardness and PH is that, even if you do it slowly through the natural way, one partial water change can suddenly restore the water to to its original state. It can be a problem if you have changed the water hardness and PH too much in the first place even though the process was slow. However the problem can be solved if you use RO water. It is the best to use commercially available product to restore the water buffer (minerals etc.). Seachem has a few good ones just for that purpose.
I like T5 lights better, but it is because I want to have the option of having high demanding aquatic plants. Some plants need stronger lights than others. It is entirely up to you what plants you get, and get the necessary lights accordingly.
