Sorry, I can't help with original prices.
You might also want to surf on over to the Apple II Documentation Project for more details about hardware:
http://mirrors.apple2.org.za/Apple%20II%20Documentation%20Project/
No, it's RS-232 serial.
Printers, modems, etc. ;-)
No.
This is a CP/M card. It contains a Z80 chip to run old CP/M software.
I'm not sure what you are asking. You just need multiple drives and multiple Disk ][ cards to use them. You can plug in two disk drives per interface card, as many as you have open slots.
Expansion cards often came with software built in - ROM in firmware. Sometimes they required external software (CP/M boot disks for the Applicard, for example). It really depends on the card.
Yes, it will stress the power supply to fill up all the slots if you aren't really using the cards.
Performance-wise - no. As you noted, some software will make assumptions about which card is where, so some standards are good to follow. You want to avoid plugging much of anything into slot 3. (A card without any ROM onboard will in general be ok, as it wouldn't collide with the built in slot 3 80 column firmware.)
It'll be exactly the same as it always is. This is a reasonable treatment of the subject:
http://en.wikipedia.org/wiki/Apple_II_graphics
You don't. There are fundamental, magnetic differences in the way the data is recorded.
They won't work. ;-)
I guess that depends on how much coding you plan to do! You only get about 32k for BASIC no matter how many memory cards you have plugged in. If you need more than 32k - then you need to do some tricky things like chaining, segments, etc.
It makes the screen twice as wide (or, put another way, it makes text twice as squished in the horizontal direction). So, it affects the way a program looks rather fundamentally.
Jump in and start playing. Don't worry about learning everything all at once.