Help installing powered sub to factory JBL navigation head unit. 2010 prius

I'm planning on installing a powered subwoofer to the factory JBL sound system. First off, looks like I'll have to tap into the speaker output on the amp located under the passenger seat.

1. I'm planning on using posi taps as they seem to be the best of the easy/non soldering options. What guage are the speaker wires coming out of the JBL amp so I can purchase the correct ones?

2. Does the JBL system have a "bass roll off", where the bass stops increasing along with the other frequencies at a certain volume level? I might consider a lc2i if so.

3. Some of the powered subs I'm considering require a remote turn on lead as well. Is there a wire I can tap into at the JBL amp since it is easy access. If so which on is it? cannot find any info on this searching the internet and i would rather not buy the lc2i if there is no bass roll off.

Thanks for your help and any other tips or info would be appreciated!