Difficult to say if buttons are too small or too big, all hands are different and button's feeling is kind of a personal thing. But I find the buttons perfect for me and easy to operate.
Internet is too basic but hey! Is an eink ereader not an iPad. I'm ok with the interface but I usually buy or download from my PC. maybe if you do the same would be easier for you, after all you should spend more time reading with your Kindle instead of browsing Internet, right?
Give it some time, you will love it.