Ok, i hope someone here can give me answer that satisfy me:))
so i have car, older car, and i have there sony xploid,(radio with cd/mp3) which has 4x50 w .
in front doors are original speakers, connected on 2 slots.
i will mount also 2 speakers on rear (under rear window)
i am looking on
Im not a sound technician but i did alot of things when it commes with audio stuff , specially for cars.
I have a subwoofer and a amp. from Magnat so i can tell you they had a bit of pumping since i have them .. they are not the best audio equipment around but for the money i give for them they are perfect. I used 6 blaupunkt speakers for the doors and the back, and i think they are cheaper then the magnat ones, they have 3 years by now, you can hear the difference that they are not brand new but since all the time i listened only from loud to verry loud with them i can tell you they are verry resistant and does have good sound performance. I have seen yours speakers from the link mounted on a car and i can tell you i was not that impresed, they sound verry bad even with some settings and enhancements from the cd-player [Head Unit].
Now to answer your questions...
1.Technically you dont have exactly 50W on a chanel is rather 4X 25/27 W depending on the product it can go to higher but those are not so cheap and im thinking you dont have the latest model from the market.
It will power your speakers, but be carefull when you mount them + - does make a difference especially for the bass, if you mount them rong they will sound a little weird.Make shore you use good strong wires to conect them, if you dont have the old wires from the factory.
And if you plan to buy those speakers you dont need a amplifier for them , they will work just fine with your cd-player
But my opinion is to go for the blaupunkt if you want something cheap and good.
//sorry for the mistakes i made , but english is not my native language.