Regarding scope feature selection, is it worth the extra $$ to go up to 2500X? I do want darkfield, though I don't know if phase contrast is worth it. Which is more advantageous - phase contrast or higher magnification?
The higher magnification can help, but does not make a gigantic difference.
The main thing to remember is that you want a 100x objective.
That, paired with 10x eyepieces will give you a total magnification of 1000x.
They don't make objectives higher than 100x.
So to get a total magnification of 2500x, the eyepieces would be 25x rather than the more typical 10x.
This does not provide any additional quality. It's akin to digital zoom on a camera; it's just making the image larger for you to see, not actually creating any additional magnification of the object.
25x eyepieces shouldn't cost very much, but personally, I'd stick with 10x.
I've never used phase contrast, but the images do look really good.
Very expensive though.