The most basic thing you need before building almost anything is a plan. Build your audio system around one or two things you like most in music (regardless of the type of music you listen to!). For instance, if you love bass, then build a system around getting the best subwoofers, researching bass traps, eliminating the 50Hz bass bump in your room, etc. You'll take on a different approach if you're a treble guy or a silky midrange guy or the tube guy, or the heavy metal & hard rock guy.
Example -- I wanted a big, dynamic sound, so I have 3 subs and high-efficiency speakers with 12" midrange drivers. I wasn't gonna get a big sound with 6" drivers, regardless of the brand or style, so I stopped wasting time and money on "small" speakers.
IMPORTANT -- do not include a budget in your plan. Most audiophiles spend more money than they want to, so don't impose a money barrier. Hobbies aren't meant to be rational.