calculating speaker needs
 

Sorry if this seems like a stupid question to most of you. Totally new to this and up until a week ago had no clue about any of it. Now, after a week of reading, I have a general grasp on most of this stuff, but still lacking in a few areas..and you know what they say about a little knowledge being a dangerous thing....
a brief background: Due to an unfortunate incident involving coolant and a head gasket my truck is no longer with us (may it rest in peace). As it turned out, my brothers mother in law was getting rid of her Dodge Caravan. 1998, as dead stock as it gets. it's no prize, but it runs and it was free (yes, free).

I'm not looking to dump thousands into it and figure if I get 6 months out of it then I'm in good shape.
Looking at putting in a sony deck and 4 speakers (5-1/4 in dash, 6x9 in rear)
I had thought about an amp and just found a cheap 4 channel one online. My question is... Do I need to add the RMS output of the head unit(17 watt) to the RMS output of the amp (200 rms. I'm assuming this get's spit into 4 = 50 watt/channel?) to find out what RMS I need for the speakers? the 6x9's are no problem, but was a little concerned about the 5-1/4's I was looking at

Need more info.Are they stock speakers? Whats the amp rated at? How are you going to wire everything?If you already have everything ,don't use the headunit for power-you don't need it.200 watts RMS is more than enough to power what you have as long as you don't like your music loud.If you do the speakers probably won't be able to handle the power,they're junk.