I would suggest you to make the installation by a professional. If you know a lot about car audio and have lots of free time then go ahead. It is getting really complicated when rewiring the whole car specially when you have 8 speakers on an amp.
Can't help you on the size of the speakers...
The Alpine head unit is a good choice but I would take a look at other brands, depends also on the style you like and would like in an E series.

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