If you want to fully power that sub then you HAVE to do the big 3 upgrade. You would also HAVE to upgrade your alternator.

I said you HAVE to do these things because without doing these you will not be able to fully power your amp. Your stock alternator would not be able to provide that much power and without the big 3 you would not be able to get that much power to your amp anyways.

I would recommend buying the FI BL instead of the BTL if you are not going to upgrade these. You would end up saving money on the sub. There is no point in getting the BTL over the BL if you are not going to fully power it.

1000w RMS is still a lot and you may still have some power issues. You may not have to do the big 3 but it is never a bad thing to do. Out of all the upgrades you can do it is the easiest and cheapest.

Instead of buying an extra battery save your money on a high output alternator/big 3. The alternator is what powers you system and all electronics when the car is running so it is the most important upgrade you can do. A battery is just an energy storage device. If you are not creating electrical power to keep it charged then it won't do you any good. The big 3 is a must if you do upgrade your alternator however. A high output alternator is going to be costly but if you want to run a big system it is a must.

Good Luck!!!

Edit: One more thing… don't waste your money on a cap