I say this every time but I’d do a bit of research into speaker theory before spending your money as you will get a lot more bang for your buck.
Off the top of my head the things I think you should reconsider are.
1) The full range box plan. Each different driver should really be self contained (as Raj mentioned) so it would make sense for you to actually build a couple seperate boxer to save you hernias and also allow for greater flexibility when expanding.
2) A 1300w amp is not a 1300w amp. It al depends on the impedance of the load its driving so while it may do 1200w at 4 ohms (I assume its a cmark 2650 if you got it off MrAHC) it will only put out 700w when at 8ohms etc. SO how you are planning on running your boxes is important.
3) Piezo’s they are cheap but they sound horrible unless you really know what you are doing with them and that takes some serious EQ so youneed a decent graphic and would be cheaper buying a cheap set of compression drivers like the p-audio bmd 450’s.
4) Don’t just buy any driver for a box. Research thiele small parameters and you will discover that different drivers are designed for different jobs and should be picked accordingly. Then the box must be designed arround the driver.
Anyway I’m sorry if I sound like an idiot but as I always try to say…You get what you pay for both in time and money. I mean we use amps that are almost 20 years old in our soundsystem and they still sound as good today as they did when they were made and we have not had a sinlge problem with them. The one place we skimped was the high end when we started and we replaced it twice before we got the money together for something nice.
Anyhow good luck and if you need any more help then get in touch.