Help needed for home setup, regarding access points

Hello guys, in advance thanks for your help and patience. I have taken the time to draw a diagram to help you understand my situations quicker.


Note: The length of the ground floor is probably 60-100 feet. With minimal walls/doors on the ground floor

As it stands I only have the second floor router but due to bad coverage on the ground floor I am planning to place an access point (where indicated).
I have purchased a powerline adapter to minimise cabling for a physical connection to the WAP. This is where I have a few questions that I would appreciate if you could answer.

1. Will the powerline adapter work in this way providing a physical connection to the WAP? Im a believer in wiring and dont like repeating due to complexity and signal deterioration.

In relation to the WAP:

Devices that use wireless are: 3 iphones (wireless n at 2.4ghz) and 2 laptops (wireless g). (future proofing maybe considered)
I am not that fussed with internal network transfer speeds. I am more concerned with range of wireless as internet access everywhere in the house is the priority.

2.Will a wireless N WAP benefit me in this situation or should I stick to the cheaper wireless G WAP's? (future proofing? mainly concerning range?)

3.I require a wired connection from the WAP so that my xbox can be wired to the home network. Is there a WAP that has network switch capabilities or will I need to purchase a seperate network switch to place before the WAP (from powerline adapter)?

4. I would prefer a single SSID where I can switch or the device switches from the upstairs router and WAP when signal is better at a particular point. Is this something that is possible or will I be better off with two seperate SSID's for WAP and wireless router and manually swicth between them?

5. Which WAP do you think would best serve my purpose?
was looking at: netgear wn604?

I apologise if these questions seem obvious, im quite a networking novice so any help would be appreciated. We all started somewhere :D Thank you very much