1. I presume your cable modem has an 'ethernet port' on it? If so you can buy a wireless router but don't get an ADSL one, get one that you can plug into a cable modem like...
2. You will be able to use them connected to your laptop (as long as they have the appropriate connections). Wireless replaces your network connection, it doesn't mean you lose all wires. You can get routers that have USB ports for printers, but I don't think you'll be losing the scanner wire any time soon (unless there's a product i'm not aware of!)
3. The wireless standards that you are likely to want to use are things like 802.11b/802.11g. Most new laptops are WiFi/Wireless enabled (built-in) and so will probably have these capabilities built-in. Don't worry about Bluetooth so much, although it does no harm to have that also.
4. yes - Here! Or look out for PC magazines with guides on going wireless.