Hi Fenn...  Welcome to the forum, and to the wonderful world of Krags!  You won't regret owning and shooting a Krag rifle.  You'll find (once it's working properly) that there isn't a smoother operating rifle made!

From what I can see, it looks like an 1898 rifle with a nice cartouche on the stock wrist.  Yes, it's common for the windage or elevation knobs to be broken off, and replacement sights are available.  The two holes in the stock are correct.  The upper is for the cleaning rods and oiler.  The lower hole is just for lightening of the stock.  Sometimes, people have found that there was enough of an opening between the two that the oiler falls into the lower hole, but that is not a common thing.  As for the bluing, that is pretty average for a Krag.  If you find one with amazingly consistent and deep bluing, chances are that it was re-blued... and that can lower value. 

Now for the barrel, if it's truly beyond use, then there are barrels available.  Criterion sells replacement barrels (in the white - un-blued).  These are high quality and correct, but you will need a competent gunsmith to remove the front sight post from you old barrel and install it on the new, which requires specific brazing techniques.  Also, the rear sight screw threads will not be correct (original are 8/30, and the criterion are usually 6/32), so that will require some attention.  Also, original barrels do come up from time to time on Gunbroker, EBay, etc.  I would continue working on your barrel and see if you can clean it up some more.  Keep in mind that barrels with pitting and poor rifling do sometimes provide accuracy with jacketed bullets.  Slug the bore and see what size it is.  Krag barrels can sometimes be oversize and having the correct size bullet will make a world of difference.

This forum is a great resource, and there are wonderful people here with amazing advice!!!

Where from down under are you?  I lived in Christchurch NZ for two years!

Paul