Relax. 100 w per channel means your receiver is capable/powerful. Just about any speaker will be driven fine by that. Don't worry about speaker "power" ratings, all will be fine and no speaker or amp will blow up. Efficiency ratings on speakers will vary but it just means that you will turn up your volume knob a little more or less. 

Buy speakers based on sound quality. When you find what you like then check their efficiency rating but 95% of speakers will be fine. 

Consider 2 good speakers rather than 4 poor ones. You'll have better quality sound, and much better sound staging/imaging. 

You have a stereo receiver.

It is designed to drive 2 speakers; not 4.

What you do with those holes is something you will have to work out. Perhaps you should cut out a section between each pair and combine them into two larger holes and put two speakers there.

Get two good speakers and hook them up.

I suggest the Pioneer BS-22 speakers, because they are only $100 per pair, and compare to speakers costing 3 times as much; an exceptional bargain (see the article on them in last month's Stereophile).

What are you going to use for a music source? A CD player? Do you have one?

If not, I suggest the Marantz CD-5004 CD player, which is very good and not too expensive ($350).

A fairly good and inexpensive subwoofer is the Polk PSW505, which can be had for only $200 or so.