A lot of good questions here, I'll do my best to answer some of these and maybe others will help enlighten us further.
1. Don't understand what's meant by that, the life expectancy of an iBook depends on it's treatment.
2. Hard drives can last up to 8 year with continued daily use, but depends on the usage and treatment. If it's working fine, then why replace? Unless you require lager capacity.
3. Fitting RAM depends on the maximum the unit will take. If it's a G3 then 512 I believe is the max you can add.
4. Yes you can use a USB wireless dongle on both units, but make sure it's compatible with your version of Mac OS X installed on your iBook
5. Yes, one is a later model than the other. The whiter is a later 800mhz or 900mhz unit around 2002-2003. While the more milky clear iBook is 2001.(500 Mhz to 800Mhz)
6.Could be a number of reasons, more than likely it's due to the metal plating above the drive door that has come away and blocking the door from closing. These are easily broken when the unit is taken apart.
7. Programs depend on the version of Mac OS X, if it's the maximum version it will handle which is 10.4.11 then it's dependant on the application, but mostly office, web, graphics based applications. You can download some apps from oldapps.com from web browsers to unility software.
8. You can use any external drive I believe (Don't think the OS restricts the size in any way)
9. Best would be tiger 10.4.11 and the most a G3 iBook would handle.
10.Yes I believe they are the same wattage and will fit the G3's. The only difference is the feet color (brown being G3 and gray being G4)
11. You wont be able to sync an iPod touch with 10.4 version of iTunes, but it will charge it and may allow you to download any pictures.(If it see it as a digital camera)
12. I don't think the G4 connectors fit on a G3 iBook keyboard (I may be wrong here)
13. Don't think a G3 iBook comes with Bluetooth??? A Bluetooth dongle via USB would work fine if compatable drivers for Mac.
14. Depends on what's installed and how much memory it has. Most case I've never found a problem with my G3 iBook running 10.4.11. (Tiger)
15. No, not if they are both working units and in ok condition, That sounds like a deal. Seen them go for more than that on eBay.
I hope this help.
If you need further details let me know.
Good Luck with your iBook's
I would recommend an external FireWire drive. I've never used a USB drive because FireWire is so much faster.
Your router should be backward-compatible with the 802.11b standard used by the original AirPort Card. If it isn't, here are a couple of choices:
So, it's your decision what you think would work best for you.