Your current barrel nut will work just fine. If your new barrel is the same OD for the gas block, it will work also. A word of advise here ...... I always purchase a new gas block and also a new gas tube. Unless you get fancy with 4-sided rails on the gas block you can replace them for under $50. Why? Because you can leave your old gas block on your old barrel and it will be there if you ever decide to use it again. Get a clamp-on gas block. They are much easier to deal with. I always replace the gas tube because it is $5 and I have seen them gummed up after being shot a lot and not cleaned well. As for the hand guard, unless the new gas block prevents it from fitting it should be no problem. I'm assuming it is a free float tube?
Unless you are going from one gas systen to another ... that is, from a carbine to a mid-length or vice verse you should be good to go.
Do you have an armorer's wrench, a torque wrench, and a vise clamp for the upper receiver? If not, you will need those things also.
If you can, post a pic of what you have now and a link to the barrel you are going to get.
There's a fine line between BRAVE ... and STUPID.