Your question seem inappropriate.
That's not a fast and loose usage. You should realize that there are two quite distinct uses of 'theory' in physics. One kind of theory is 'a theory'. It's a specific model for some phenomena. The kind of theory is just 'theory'. This one is a mathematical framework that can be used for constructing theories. The latter usage comes straight from mathematics, e.g. set theory, number theory. String theory is theory, as is quantum field theory. Quantum chromodynamics and quantum electrodynamics are each a theory, both couched in terms of quantum field theory.
This is a poorly asked question that tells us that you do not understand what a scientific theory is. A scientific theory has to be supported by massive amounts of evidence. So as asked your question makes no sense at all.
No, in general. There are some exceptions which we could tell would not produce a viable organism (trivially, the sequence 'AAATTT' will not produce a viable organism), but we cannot tell whether a sequence will produce something viable. Not remotely. We can't even predict with any kind of reliability what effect a single mutation will have on the tiny genome of a virus.
No, other than by looking at the DNA of closely related organisms (which typically will have similar morphology), which I don't think is what you're interested in.
There are aspects that can be directly linked. Such as finding the proteins coded by a specific section of genes and seeing how they work. But there are so many different proteins involved and we have barely scratched the surface of this new science that it appears the answer to #2 and #3 are going to be "no" for a while.
I would disagree with your value of "generation". For humans it is not unreasonable, but we have a rather long time to maturation. But for small mammals a generation can be very short. Mice, for example are sexually mature in as short as 4 weeks and at the most at 7 weeks. The live one to two and a half years on average in the wild. For them a generation would could easily be considered to be about 6 months. I would bump your number of generations by a factor of 4 at least. But then I am not a biologist.
DNA is going to degrade as time goes on. But the rate can vary greatly depending upon several factors. Number one is probably where did the animal die? If it died in the tropics with ideal temperatures for bacteria and other life it may be years in most cases. In the Arctic or Antarctic it can be much much longer. Size is another factor. A mouse will break down rather rapidly. or get consumed and break own almost entirely. An elephant's DNA could last for quite some time. It's tusks especially would protect the DNA for quite some time.
