should go step by step instead of big bang approach.

start with 2 channels.
then sub.
then surround.
then finally center (or if u have budget, get front and center at the same time).

Front channels and center should match
sub don't need to match brand
surround don't need to match brand

Reason to go in stages because you should put your $ in better front speakers (e.g. 3-5k). next year another 3k for sub.
Contrary to popular believe, it's not 70% of sound goes to center. 70% sound actually goes to front 2 speakers.

Reason: 70% of your content is in stereo (Astro, music, sitcom, tv series, sports, etc). Only 30% of the time you watch movies.