Don't worry too much about the power. Unless you were planning on having you ears bleed from sheer volume, or unless you are using this setup in a huge room you will be more than fine. You won't be using anywhere near 100 watts 99% of the time as long as you are listening at acceptable levels. That doesn't mean you cant have it loud, just don't have it deafening.
One thing to make note of is that 12 gage cable probably won't fit in the clips at the back of your Onkyo right away. This doesn't mean it isnt the correct choice, just that you may have to snip a few strands off of the wire in order to get a tight fit. Don't let this worry you, you won't loose any signal. Home Depot speaker wire is probably less than $.40 a foot near you.
As for stands, as long as these guys are tall enough then I'd say the price is right.
Speaker stands
Good luck with the new setup, It's a really decent little 2 channel rig, enjoy it.
