Don't know how to quote....but yah i guess it never did say he used magnetic gold sand.

And just because he can sense killing intent doesn't mean he can sense whose killing intent it is, if I'm not mistaken.

Night gathers, and now my watch begins. It shall not end until my death. I shall take no wife, hold no lands, father no children. I shall wear no crowns and win no glory. I shall live and die at my post. I am the sword in the darkness. I am the watcher on the walls. I am the fire that burns against the cold, the light that brings the dawn, the horn that wakes the sleepers, the shield that guards the realms of men. I pledge my life and honor to the Night's Watch, for this night and all the nights to come.
-Oath of the Night's Watch, A Song of Ice and Fire

maybe, but he did say he noticed Kakashi's chakara was missing when he first started fighting pain, and then he was able to locate pain's chakara when he stabbed himself with "god path's" rod thing

moreover flaming mode is so silly, seemed like he had better perks with his nature mode abilities - like how it made him stronger the longer he used it and how it healed him

sage modes has nice perks but he can't use it persistently without the fusion also he wouldn't be able to deal with the zetsu clones in sage mode, as far as dealing with kabuto i just don't think he has that kind of control of the kyuubi mode sensor perks or the range. remember he's sensing intent not chakra and i don't think he'd be able differentiate individuals through intent.