Just done this in my own house. There is some confusing terminology going on here, let me explain.
You only ever need one router. Conected to this you might have multiple switches with CAT 5 or cat 6 connecting them.
Homeplugs are wired, they use your houses electrical circuit instead of CAT5 cable.
You can get homeplugs that act as wifi extensions. These give full speed wifi to the limit of your homeplug speed.
Wifi repeaters bridge wirelessly to act as an extender. These run slower than wired ones as they have to accept and transmit every signal that comes into them (doubling traffic on the wireless channel).
Wireless access points however are wired in with cat 5 and can act as an extension to your wifi giving full network speed.
I bought two 5 port gigabit switches, a wireless access point and a reel of external at 6 (make sure its not CCA cable!).
Had wifi at the end of my garden for about £60.