If the Galaxy handset has been unlocked - yes.
the phone should come with a sim card which is to a specific network, if you don't have a sim card you can go to a phone shop and buy one. It should be about $5 or £3 for one.
You can use the same SIM card for your iPhone 6 that you used in your iPhone 5.
Provided the new handset is unlocked... yes you can.
Inserting a SIM card into an iPhone 5 without the tray is not advisable, as the tray is specifically designed to hold the SIM card securely and ensure proper connectivity. Attempting to insert the SIM card directly into the phone without the tray could damage the device or the SIM card itself. If the tray is lost, it's best to obtain a replacement from Apple or an authorized service provider.
Yes
5-10 usd
You just wait about 5 Sim hours and they will come back!
Assuming the SIM card is the correct size for the iPhone (ie not a micro SIM) - there's no reason why not. Since you say it's unlocked - it should accept any networks SIM card.
Yes the iphone 4 uses whats called a micro sim card it is smaller then the regular sim card out there. At www. phonetraderonline.com they can custom cut your existing sim card or provide you with a micro sim for your carrier.
The Samsung Galaxy Note 5 as of this writing is not out yet. It is in development.
Cook for 5 seconds in a microwave oven, this will do the trick.