ы and и are about as similar as the vowel sounds in the pairs pill/peal, kill/keel, dill/deal, sick/seek. etc. Not the same. You need a good textbook with a CD so you can hear the actual sounds. You can't learn pronunciation from a book.
Russian consonants (neither palatalized 'soft" or nonpalatalized "hard") are not aspirated like English ones -- there is not a puff of air iafter PTK. zxc is correct.
Й is a semivowel, not a diphthong. It sounds like the Y in "boy".
In a couple weeks you have probably not seen a million words all together, let alone one word a million times. To learn a language you must do more than read. You must write. You must listen.even if I have already seen it million of times
When I was a kid we had a weekly spelling test (in our own native English), and in preparation for it we had to write out the words ten times each. Not a bad idea for you, either.