Just looking at those products I have a couple suggestions for you...
First off there is some conflicting information about what speakers you may be using.
If it is a dual voice coil speaker with 4ohm per speaker it will depend on how you hook them up.
If your speaker leads are connected in serial (One lead goes from one plus to the other negative and you tie to the other + and -) then you are running at 8 ohm total for that speaker.
If your leads are connected in Parallel (Wire running to both + and another to both -) then that speaker is running at 2 ohm.
With same thought in mind... If you run the speakers in parallel (same wire to each positive connection on the speaker, another wire to each - on each speaker) you will half the ohm of the speakers.
With same in mind if you series the speakers (Run one wire to the pos on one speaker, one to the neg on the other speaker and a wire from the neg of the first speaker and to the pos of the other speaker) you will double the speaker ohm.
So depending on how your speakers are hooked up you could be putting a 16, 4, or 1 ohm load on that amplifier. A 1 ohm load on your amp would be really hammering it and would likely require a much more significant power wire.
The other thing is no way you are getting 1000 clean watts in a true 1 ohm stable amplifier for under $100.
So I would suggest first, make sure you understand the different configurations for your speakers. It will make a difference on how you want to connect to your amplifier. Higher ohm generally means cleaner bass but less powerful, lower ohm generally means dirtier bass but higher output. And the draw on an amplifier is more the lower the ohm pull on it.
I would also throw out that junk amp and get a better quality amplifier. You may also want to consider going with a stereo amplifier as opposed to a mono amplifier. You may find running a good quality stereo amplifier running 400-500 amps with a 2 ohm load on each speaker sounds much better and gives you more bass. Planet Audio, Boss and some other manufacturers are cheap for a reason. You likely are getting no where near that 1000 watts they are suggesting. Especially if you only need a 4 gauge wire for it.
I have 3 12 inch Alpine subs in my midgate running ~ 400 watts apiece using Competition Audio Art 100MS amplifiers. These cheater amps put out a significant amount of wattage for such a small and now 20+ year old amp. When running at full volume you definitely notice the bass... From probably about 3 blocks away... And it sounds decent too. Not quite the quality of some other subs I have had but still really nice. (And for $50 a sub during a friends selling off of equipment when they closed their shop... Yea Ill run them... )
Oh and I am running 1/0 gauge wiring, a second battery and a second alternator. Not necessary for the battery and alternator but I have other plans for this truck too that will use that power...
Also one note about how they have those speakers configured... The Speakers are setup in a Series type configuration which means each speaker is seen as an 8ohm load. The Speaker to amplifier is in Parallel so because the speakers are set to 8ohm apiece the amplifier is seeing a 4ohm load. You COULD also wire that amplifier up with a wire jumped on each speaker to both positive leads and both negative leads but I suspect you will find that amp crying about a 1 ohm load even though it says it will handle it. Running at a 1 ohm load instead of a 4 ohm load should be considerably louder but I would seriously doubt a 4 gauge wire would be enough.