Alpine HU have been good for me.
The 143BT gives you two outputs which leaves room for expansion later. One for speaker amp, one for sub.
Consider the 147BT as it has 4v preouts instead of 2v on the lower models. 4v is twice the input power going into the amp. Theoretically, if the HU and amp are matched and tuned properly there should be no difference if using only one amp but the extra signal strength can make up for weakness like less quality rca cable, longer runs, and multiple amps. Don't know the retail cost difference.
No experience with the KTP-445 but the HU you are considering are already rated at 50w so I don't think the KTP is a beneficial choice. An independent amp usually sounds better than HU power but there are stronger amp choices for similar $$. Don't be distracted by built in rca and output pig tails. You still have to run wire and will run better wire than the ultra thin that is part of that proprietary pig tail.
You don't specify what speakers are currently installed?
Any time you add an amp or plan on listening for longer periods with engine off, I recommend a second battery if not so equipped already.
1991 MariStar 240sc, 454, tower, WetSounds, Krypt and Rockford Fosgate