best way is to tap into rear speaker on same side as you will run your power to the battery. That way you dont have to run wires down both sides of interior. you can remove the sill plate and run cables
I ran my power wire thru the clutch cable hole behind the pedals and to the battery (remember to put an inline fuse)
luckily, the radio already had the orange wire (on when radio on) tapped into
when I did my subs (before I sold them) I used a speaker box since I wanted more than one sub
the hi-lo converter worked for me as my amp didnt have speaker level inputs
I ran 2 kicker comp vr 10's in a sub box with an MTX amp powering it...man THAT SLAMMED