Hashem is, first of all, beyond our understanding. EVERYTHING that we see, think, hear, understand etc; including time and space; is all part of Hashem's creation.
The Gemoro learns from the Torah that we can give descriptions about Hashem 'כביכול', but it says that without learning it from the Torah, we wouldn't be allowed to give descriptions about Hashem.
So you say that if Hashem is perfect, them he has no choice and no free will other than to be perfect. What you're doing is what all people do which is understanding Hashem similarly to how we understand other things. In truth, the concepts of 'perfect', 'choice' and 'free will' are all creations, and and therefore don't really apply to Hashem.
Robots have no free will. Therefore, to praise them when they help you would be meaningless. Similarly, if you held a gun to someone's head and asked them to do something for you, thanking them would also be meaningless. But Hashem of course isn't bound by these limitations. He has the choice to do whatever He wants. He's a supernal being, beyond emotions and intellect; and He can do whatever He wants to us.
(He made us, chose us as a nation, and while he doesn't need us or our praise as he's infinitely greater than all, he wants us and our praise. (Michoel's answer quoted this chassidus based article: http://chabad.org/library/article_cdo/aid/248150/jewish/What-Does-G-d-Need-Us-For.htm))
Is He perfect? Well, in the language of humans, yes. Whatever He does is perfect, whether He makes the sky blue or red, whether He makes people live or die, it's His decision, and He Who made the word perfect decided that He will always be perfect, whatever he does.