My 2 cents regarding your questions:
I've going through almost the same questions and found some answers that matched my needs. First, the first place to check for devices is Ebay, they have a lot of product that could be very interesting price wise.
For example, I got the Russound A-BK1 for $560. IT is retailling for a $1000. Quite a bargain for an excellent product in my sense.
So for your question:
Ethernet network and Phone.
Two runs of cat5e is definitly the minimum to go. the way you are describing it is correct. The only things I will add is to be extremly careful when you run the cable. No more than 25 pounds of pressure on the cable (cat5) otherwise you are damaging it. Be careful to stay at least 6 inches from any power line if you are running parallel. If you have to cross a power line, try to have a 90 degree angle on the cross.
One thing you might consider is an extra run of Cat5 from your bonus to every room for the IR dispatch.
If you have a distributed audio system in the house, being able to control them from any room usually avoid running up and down back and forth to change the radio station or to skip a title.
For the connection, Leviton is doing some nice "boxes" that contains everything for video/phone/network distribution (http://www.leviton.com/lin/index.html
The other benefit is the price. Pretty friendly. If you want to go fancy, you still use a patch panel but it's a little more complicated (yes not that much). I personnally have a 96 ports patch panel for phone/network distribution and I was thinking using it for audio and IR dispatch. One more time some shoppping on ebay ($40 for the 96 ports).
The easiest solution I've found so far is to use the Russound ABus system from Russound. It is really nice if you as me. Actually I'm completly sold on it. It is carrying the sound signal through a cat 5 cable to the keypad. The keypad is performing several functions at the same time. It is amplifying the signal so you could then run speaker cable from the keypad to the speaker. They have a line output too if you want to connect a real amplifier. Drawback only two channels could be sent.
The eypad is performing an other role too: it is an IR dispatcher. Meaning that you could use the dedicated remote for changing the sound volume but you could dispatch the IR codes for the receiver from one room to your receiver in a different room.
The kit runs for about $560 on ebay these days.
Channelizing is the easiest way to go but you have to keep in mind that you will loose any encoding of the sound beyond dolby prologic. There is several solutions but channel plus seems to have some basic equipment that could channelize from 2 to 4 video stream.
One of the thing I didn't really completly solve for the moment is the coupling of the audio dispatching and video dispatching. Since they are two difference systems, they don't seem to be well integrated.
Less fancy than channelizing is to have a video selector with a channel 3 or 4 modulator behind. What ever element is selected could then been sent as channel 3. You could even have 2 modulators one for channel 4 and one for the channel 3. You could then put a combiner and you're done.
By the way, a splitter used "backward" is a combiner! Just realize that a couple of weeks ago!
If you have any question, feel free to send me a mail.
Good luck with your project,
Frederik Delacourt www.bigfoot.com/~fdelacou/hometheater/main_en.html