Number 1...Any hex for 90 bucks is pretty much a good deal. Now the question is do you have a C&R where they can ship it straight to you? Because with a shipping and transfer fee to someone with an FFL, we're talking about 50 bucks added to that 90 dollars.
Number 2...I have shot steel cased ammo in 10 different Mosin Nagants, and have never had an extractor break. Who told you this was a problem?
Number 3...Hot soapy water is probably the best way to clean corrosive residues, though I just usually swab them out with patches and Windex, then give them a normal cleaning.
Number 4...The best scope mount is probably a drill and tap one, though you will probably have to also get a bent bolt if you go that route. Since I frown on doing a permanent change to my Mosins, I went with a Scout scope mount and long eye relief pistol scope. That way I can reconvert it back to stock if I ever want to sell it. (Though I can't imagine why I would sell one)
Number 5....No there is probably no cheaper ones out there with better accuracy. I would go with Finns if you want better accuracy, but they are not cheap.
People think I'm paranoid because I own guns. If I own guns, what do I have to be paranoid about?