u/CALAPU

I just started my research, but would someone be kind enough to enlighten me the possible upgrades for the sound system in this?

I am coming from a Nissan Altima SR, and all I had to do is buy two door speakers and two kickers in the rear (All Rockford) ... with this vehicle it seems way more complex.

If it is as easy as just professionally installing a subwoofer, maybe some recommendations for what brand and size would do it justice.