Need some hardware advice for noob to get started...

Hi,

I've read a bunch of the threads here trying to get an idea of what I need and am starting to get an idea but am still confused between everything that's out there. Can someone point a few clues where I can start digging.

Goal: Have a long building (1 floor) which I would like to put wi-fi throughout so I want to extend wi-fi from one end to the other (300 ft est). [The building is not deep, just long]

[----------x--------------------------------------------] [--------------------------------------------------]
^
router here

Currently the connection goes only to x, I assume because of the walls.

The router I am using is the one provided by the ISP an ADSL router (Siemens gigaset se567).

Can someone tell me if this is the direction I should be looking at:

1. Get a wireless n router and plug router into the new router.
1a)Get a directional antenna to help with broadcast of signal?
2. Get a few extenders? It sounds like an access point can serve the same function as an extender? (Access points require wiring to serve this function?)

Solution?

[-----------y------------y------------y---------------][--y----------y-----------y--------------y------------]
n-router

y=extenders

Questions-
How far does each extender extend? How much does the signal degrade as it extends.