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Most seeds do not need light to sprout, though there are a few that do. Most seeds that need light to sprout will have this very clearly pointed out in their sprouting directions. Once the seeds sprout, then all plants need light of some kind. Some plants need more than others and some can take very low levels of light, but all plants do need some kind of light.

For optimal growth, yes, a warm and a cool are best, as they will provide both the blue and red light spectrum the plants need. That being said, for the most part, especially if you are just growing seedlings under the lights, cool bulbs alone will work just fine. The plants grow fine and do not suffer from the lack of the red spectrum for the relatively short period they are under the lights. I would only worry about making sure they get warm light if you plan on keeping them under lights for many months.

This article should help: https://www.gardeningknowhow.com/plant-problems/environmental/how-light-affects-the-growth-of-a-plant-problems-with-too-little-light.htm

This really depends on the plant but normally too much light can cause foliage to curl and may lead to scorching of the leaves as well.

When I googled "fixture for VHO 96" fluorescent" I found a number of sources. It may take a bit of research, but you should be able to find what you need. There are so many possible lay outs of artificial light for growing, and so many different opinions on the merits of one system over another, that the best advice I can give is to do as much research as you can, then try a set up that seems good to you. I do know that I prefer fluorescent light to other types of light sources, for anything I've ever grown. And I'm very interested to see what kinds of results can be had with new LED technology.
Here's an article with general information: https://www.gardeningknowhow.com/houseplants/hpgen/fluorescent-lighting-for-indoor-gardening.htm

Here is a few links for you.

https://extension.missouri.edu/p/G6515
http://www.uvm.edu/pss/ppp/articles/lighting.html