Hello dbalsx, and welcome to the friendly Camera Labs forum!
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Unfortunately I cannot advise you regarding the adapter. I have an adaptall-Nikon adapter but as there are no manufacturer markings on it I'm not sure who built it.
As to exposure-metering: it works on a D300 and a D800 by entering the f-number 8 into the camera. I doubt the D5100 has this capability.
And regarding tele-converters: Yes, the lens "looks" like a Nikon lens mount-wise, but Nikon TCs don't accept every lens: it has to be "TC-enabled". The Kenko TC should have no such trouble, but you have to check whether the front-side of the TC fits into the back-side of the lens without damaging any elements. Better try with extra caution before you buy! I never tried my modfied Nikon 1.7xTC on the 500/8.0 but I doubt that you will be pleased with the optical results.