hertz he4 is a good choice. it's 400 rms . as you are planning to put either front speakers or sub later apart from rear ones , i would suggest you to buy amp with preout , in case you plan to buy one more amp for further upgrades you will need preout
speakers you told is good for sound quality. but it wont be very loud i guess.
for surround sound go for comps , which will be costlier.
normally , the final expense for the products you told should be around or less then 26-27k.
if you want to stick with rockford , this will be a good sub for some real kind of bass production - http://www.rockfordfosgate.com/produ...n_US&p_status=
hi-low converter will be placed by cutting and connecting it to the output wires that comes from HU.
Grounding wire must not be very long. it should be as short as possible. and grounding wire should be properly connected from amp to the metal chasis. You can use bolts that is piercing through the metal part(chasis) of the body as a terminal point of grounding wire.
Sorry if my language is not so technical as i am not an engineering but a medical student.