A lot of answers will depend on what you're shooting at and when.
Adjustable objective. Is it worth the money?
It's almost a given on scopes with fairly significant magnification range. It's not neccesary to use it for the majority of hunting but all you need do is set it at 100 yards and forget it exists for any shot from 5-200. Anything farther and you'll have time to make the adjustment or you don't have time for the shot.
Side focus. Again is it worth the extra money?
No, but it's the same adjustment, parallax, not "focus".
40mm verse 50mm. I assume it collect more light, but is there any other benefit.
No other benefit and 40 sits closer to the rifle which almost always means better cheek-weld. You can get 40mm objectives that are better than 50s too. It's glass quality and coatings, not size.
I've used a couple Leupolds and a few Nikons. The Nikons don't compare in light-gathering. They're a decent scope for the money but the ones I've used have been near the bottom of the pile in low-light use. The Nikons I've used were all on the lower end of their price range but they don't compare favorably even to other low-end scope, say nothing of the higher-end Leupolds, Sightrons, Bushnells, etc.
Still happily answering to the call-sign Peetza.
The problem, as you so eloquently put it, is choice.
He is no fool who gives what he can not keep to gain what he can not lose.
-Jim Eliott, paraphrasing Philip Henry.