In my experience, completely stripping paint or varnish from newel post and each and every spindle is about 10 times as much work as you imagine.
Thats a lovely newel post. I would find the mismatch with the stairs irritating.
My suggestion would be, strip that, and the banister rail, and oil them.
Then clean, but not sand, the spindles, paint them with Zinsser Bin.The only paint in the universe that will stick properly to varnished wood without sanding it first.
The colour mismatch of the banister rail and the newel post? Once stripped, so your eye is drawn more to the grain of the wood, it might not matter so much. If it does, you could stain the banister rail darker ( although don't imagine you'll get a colour match-making that's v tricky).
The order must be strip, any staining, paint, then oil the newel post and rail - ( drip any oil and the paint will have a harder job sticking).