Do you have an amp to drive the splits?
Here is my thoughts and many will disagree, but I am still going to give my 2c.
Use the Dixon head unit and buy those kicker splits. It's better than having nothing in your car.
Buy a 4 gauge cabling kit, decent one.
Buy a decent 4channel amplifier. Install amp and wire kicker splits to amp.
Buy a decent head unit and replace the Dixon.
Buy the sub you want with a box and connect to amp.
This can be done as you have money for the components. If you can, give an amount you want to spend on each and we will post, what we think, the best component is you can get for that amount.