First I'd like to you to SSA, you found the right place! I agree that an Xcon sounds like it would be right up your alley and the SAZ-1500 is a great amp to pair it with. You're going to want to do the big 3 to start. I actually do this on all vehicles no matter how much power is being used. If it can be worked into the budget, it is always a good idea to upgrade the alternator, especially if you think you might someday add more power. You shouldn't need an HO alternator necessarily but without one you will likely need to add 1-2 batteries. Going with just batteries might be a bit cheaper but you also have to find a place to put them and that may encroach on your available space for amp/s and sub/s which is already limited. Due to the size and shape of the trunk, I would pretty much forget about trying to get an 18 in there and even a 15 might be tough although without some numbers to go by, we're just guessing here. When you get a chance, try to get us some max dimensions inside the trunk so we can help figure out what size box will fit and don't forget about the opening, you have to get the thing in there after all. The box could be built inside the trunk if necessary to maximize airspace in the box but I don't know if that is something you would want to do. Get those numbers to us and we'll be able to better assist you.