Starting from SCRATCH whole home system indoor&out

My dad is putting in a stereo system and is getting advice from one person. He lives in the boonies, so I am concerned that he receive a limited amount of information. I am hoping to bounce ideas off of some of you to make sure that he ends up getting the best quality system for his money -- not just a system that is convenient for his contact.

My experience is fairly limited. I have a Denon 3803, that I found used still under warranty for $600 a few years ago and two B&W 602 speakers. I am adding on gradually as I can afford to. I suggested that I've been happy with my receiver and that he may want to get the same but wanted to get your thoughts...

Here's my dad's situation/needs:

He would like a surround sound/home theater system in the main room and to be able to power music outdoors in two separate locations (front and back yard). I have found it convenient to be able to have a movie on inside and listen to music outside at the same time and I imagine he will want the same.

Here's my dad's first message to me:
"Victor proposes to use a Denon receiver 100 watt 7.1 channel then put a booster on to power more speakers. He says to go bigger starts to cost a lot more money. Also his speakers are Canton’s – he feels the aluminum is much better than the polyprop. When you have a chance, give me your thoughts."

And his second message:
"Thanks for looking at this. It’s a Denon AVR 2807 $1000.00 AV 7002
Canton, AS80SC Canton, 2 pairs Plus X2 cantons, OES one Speaker Craft
outdoor, VBX Speaker Craft Table top Volume remote Control and a MX850
Universal Remote. I asked him to price me a DVD/VHS unit and a CD
player. Also do we need a DVD burner? I don't think so."

I don't know anything about Cantons -- have never heard of them before -- nor do I know anything about aluminum vs. polyprop. How do people feel about investing in the Denon AVR 2807 receiver? Also, how do people feel about buying used, as I did. I have seen more 3803's, like mine, available for $500 said to be in perfect shape. Perhaps I got lucky, or perhaps checking out the unit and running the serial number by corporate to make sure it is legit is a reasponsible way to buy?

Also if there other sytems/speakers that you would recommend I am interested to learn your thoughts. 7 years ago after comparing many different brands of speakers I decided to go with the B&W 602's... but I'm not sure where things stand today.

Thanks in advance for your thoughts!

-- Douglas
Buying used can of course save a lot of money. For new recievers the price new often is very discounted with perhaps better features as well. Denon, Yamaha and Onkyo etc all have good gear. Best to focus on ease of use. And units that will give you the remote zones you require. A speaker selector box may suffice for a third zone if needed. That will be more important than ultimate power. Some of the more top of the line units have more the one remote. Having a after market one may not be needed. Speakers are of course what sounds good to your ears, but Canton's a fine line of speakers. Hope this helps. Glen