1. The Fusion is more than adequate for any HD movie watching and runs Windows 7 with ease. I have the E350M1, along with an Intel SSD and 4GB of ram, and it works like a champ. The D510MO Atom board is also great for a carpc, if you want to stick with Intel. Just remember that you can't legally watch videos in the front seat of your car unless it is in park.
2. 2GB is fine. Windows 7 32 bit can only use up to 3GB, and Windows 7 will run just fine with 2GB. I only have 4GB because it was cheap at the time I bought it.
3. If you want to stick to your budget, then you'll need something with at least 400nits, like the 669GL high brightness version. If you can somehow recess it a bit, that will help block some of the direct sunlight.