1. Yes they do tend to be more slender, but trust me they still have plenty of "heft"
2. Yes
3. Are we talking adult or baby? A good K. albino will run around $150-$300 add arabesque and you are looking at $500-$1000
4. I like the boaphiles cages, and a 4x2 should be perfect for an adult male
5. Although I have never owned an Argentine they do tend to have a little attitude, but nothing to major (from what I understand...others who own/breed them could probably give you some more insight)
6. The different local's do tend to vary a little in terms of attitude. Just remember the "pure bred" animals are closer to a WC animal than a random redtail. Therefor they can have a little more attitude than a general BCI

If you like the speckles an argentine would be a good choice as well as an arabesque. If you like albino save up and get an albino arabesque, you will be very happy in the end!