Living Room:
You can get that Oppo H31 for $1500 Cad including tax & shipping, it's a good deal at that price. For a DVD player I'm going to say Panasonic S77 for about $300 Cad, pick up this months Sound & Vision to see why. Marantz 7400 at $800 or less would be my receiver suggestion. As a backup there's the Pioneer 1015 @ $700 CDN and the Yamaha 5860 @ $700 as well. You can get both on sale for at least $100 off every other week. You may want to throw some more money at the receiver and step up to the Yamaha 1500 for about $1000. Budget at least $700 for a screen.
Some things to look for in a projector include: Native resolution, Native aspect (16:9 is best for a HT), lumens (how Bright), fan noise, connection options (component, HDMI etc) contrast, mounting options, etc, etc, etc RLA, BMXtrix, and Brian are really some of the guys to give you all of the info you need here, but these are some starting points.
Parents room:
Yamaha 5830 $299 (you can get it for $200 on sale), pioneer 588 dvd player, $150 at Futureshop.
I am 100% the wrong guy to ask about multi room/source, so I'll leave that for the experts.
So my advice is this:
Oppo H31 :$1500
Marantz 7400: $800
Panasonic S77: $300
Screen $700
Total Cost for HT:$3300
Yamaha 5830: $300
Pioneer 588: $150
Total Cost for parents room: $450
That's $3750. If you use your max budget of $4500 that leaves $750 for the rest of your needs. Plus by shopping around you can knock off $200-$400 off of my suggestions easy. For a screen you really should contact some local shops. Brokerage fees, taxes, etc make getting a screen from Carada much more expensive here, otherwise I'd suggest them. You may be better off if you can get a kit and put the screen together yourself.