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As far as Tethering goes, I have the 6GB Share Plan which allows me to share 6GB of Data with my other Devices. Now if I go over 6GB it will be $15 per GB. With Tethering I can use as much Data as I want for Free

I basically have Unlimited Data using the built in Mobile Hotspot for Tethering other devices to my SGSIII . You can get Tethering from here:
[MOD][VRALG1] Enable Stock Mobile Hotspot (Tethering) - xda-developers
The way I understand this is with the new Share Everything Plan, you can tether for free. However, your data cap remains at whatever level you've set it up to be when you signed your contract. Therefore, you really don't have unlimited data and will incur that $15/GB charge for anything over your cap. Your cap is pretty substantial but I don't know how many devices you have attached to the plan. You could probably exceed that cap by tethering without too much trouble..
Yes. With Verizon's new "share everything" plan, you can use Mobile Hotspot all you want, but you still have to stay within your data allowance.
Previously, when unlimited plans were available, you had to purchase an additional plan to use the builtin hotspot, but now that data is capped, you're free to use that data however you see fit (mobile or tether). Now, back with the unlimited plans, the advantage to rooting and using a 3rd party tether app was that it masked the traffic as "mobile" data, rather than "hotspot" data (excuse me for not knowing the technical terms), so you could avoid the additional mobile hotspot fee by using them.
So, unless you're still on a grandfathered unlimited plan (or any "old" data plan), there is really no difference in what you use...builtin MH or 3rd party tether app. If you're on a "share everything" capped data plan, don't think that you're getting anything for free! (I'd check my data usage to be sure).
I believe the link you posted is simply a method to use the builtin MH without it checking for a subscription (which you would need if you are still on an "old" data plan).
Of course, this is just my understanding, if anyone has information to the contrary, please feel free to chime in and correct me.
I am still on unlimited data so I don't have free mobile hot spot. Would I be able to tether / mobile hot spot?
If you rooted and installed a 3rd party tether app, yes, you could. Do be aware, however, that by doing so you are in violation of Verizon's TOS. I've never heard stories of them bringing the hammer down on anyone for it, but it's not like I've done much research into that subject either.