A 140a alt is a pretty nice upgrade.
You'll definitely want to upgrade the alt wire and grounds if you run an amp. The amp will need 4 awg, so it'd be good to upgrade to the same.
That amp would definitely be a better choice, if for no other reason than Skar is a known company. They're low end, but their amps do make the power they claim. You'd need RCA (low level) inputs to use it. It's unlikely the head unit has RCAs, so you'd need a line out converter or two. Something like this.
The listing I find for the amp on amazon shows a bass knob. Looks like a phone plug connection.
As far as the LOC is concerned, Steve Meade went on a deep dive as to why the market is flooded with bad products. (part 2 of LOC reviews) Steve Meade really liked this Kicker model. As an added bonus, the Kicker LOC will also give you a +12v remote turn on lead.
EDIT: the kicker will take 50w input. So be aware there is a limit. If the signal you're sending is bigger, get the AudioControl.