Hello HAF! I'm new to the site as well as the new owner of a 2017 Honda Accord Sport SE. See picture below.

I'll go ahead and say it has the 4 speaker system which is pretty bad considering what I'm used to. Hopefully this thread will allow me to answer all of my questions.
My first question is: What will cause me to lose my new car warranty in terms of upgrading the audio system? I did a quick read up on
Edmunds about warranties being voided but I know that some installations require heavy wiring and alterations to the vehicle so I wanted to get HAF's opinion on what I should be aware of.
The first thing I wish to do with this car is to put a sub in the trunk. After speaking with a Crutchfield rep (Dolly; she's the bomb) I've settled on
for my trunk. I don't need competition speakers and I like the idea of having everything in one place. Also, the *** included is a must for me so I figure this is a great deal. I'm open to suggestions however so feel free to make a recommendation if you feel strongly about a particular sub.
I'm also considering replacing the four factory speakers as well but to be honest, I have no idea where to even start looking. I trusted a friend to make recommendations for me the last time I purchased the subs for my old car and while his recommendation was great, I'm still no closer to being able to match what I need with what is available. Any overall advice for purchasing speakers would be greatly appreciated.
Thanks in advance!