Mike,
You will love building a flintlock!
Pardon me for assuming, but based on your title and question I am going to assume that you have not built a muzzleloader before. If I am wrong, then my apologies up front.
If you have built a percussion gun, you will probably find a flintlock build to be slightly easier.
With that, assuming it is your first gun build, I think you have the cart before the horse a little bit.
Start with its intended purpose. You said targets and hunting. Make sure you know the minimum caliber in your state for what you intend to hunt.
Then choose a style of rifle that you like, and will fit you (and your budget). Is this gonna be the only gun you ever build? If so, don't rush. Go to the local gun store or muzzleloader club and shoulder some rifles to see what fits well. As an example, I don't like deeply crescent butt plates. I didn't know that till I built one. Oops.
There are lots of resources on different styles of historical guns to choose from.
I love historically correct guns and try to build them that way, but that doesn't mean you have to. Build a generic gun if you like, and if it done well and fits you, that is about all you can ask for on your first build
Next, decide how complex you want the build to be. Do you have wood, and metal working skills and tools? If no, are you willing to spend the time and money to get them?
The options range from buying a custom gun built but left in-the-white (need to sand, stain, polish, etc) , or a assembly kit like from Pedersoli, or get a pre-carve kit from track of the wolf or Jim Chambers, or finally, build it from a blank.
The tools and skills you will need progressively increase as you move down that list.
Since you mentioned looking at barrels, it sounds like you are considering buying parts piecemeal to assemble a gun. That can work, but you gotta do the research on style and building first. Otherwise you will almost definitely waste money on the wrong parts or build a Frankenstein-gun. Nothing wrong with building a gun that doesn't conform to a classic rifle style, but without the right combination of parts, it will not look right.
Lastly, buy gun building books! The Gunsmith of Grenville County by Peter Alexander is great. Recreating the American Longrifle is great and there are others.
There are also videos out there. They are awesome, but I think they complement the books rather than replace the books.
And of course, this forum. Lots of folks way smarter than me out here.
If I have missed the mark on your question or experience level, then at least maybe someone else will benefit!
Edit: okay, I'm an idiot. I just re-read your post and see that you intend to fabricate the rest of the parts.
That's a lofty goal! Do you intend to build the lock?
Anyway, I will leave the first part of my post up un-edited because it may still be relevant.
Again, choose a style and go from there. I would also then consider trying to copy furniture of a particular style and keep it consistent. Otherwise, Frankenstein-gun.
Look at barrels from Ed Rayle, Colerain, Rice or Green Mountain. You could also look at which barrels come with Chamber's or Track's kits of each style and then get that barrel.
So I don't risk failing to understand your question more, I will shut up now!
Cheers,
Chowmi.