A replacement (insert) window fits inside the existing window frame. This allows for minimal disruption of the existing interior or exterior trim. So you would not have to redo the interior trim - you can get replacement windows with would interiors but you'd still have to finish the frames and sashes to match the existing trim.

With a new construction window you would have to remove the current frame - so you remove and either replace or install new interior and exterior trim.

I'd definitely consider having the existing windows restored. You'd have to replace the fogged insulated glass unit - but only having one of those isn't too bad. I'm concerned about the crooked sashes - if that is because the counterweight is broken on one side it's not a problem. But I'd have somebody take a look at them to make sure they are worth restoring. If the original windows were poor quality or there is hidden damage that needs to be repaired it might not be worth it.

Check out oldhouseguy.com

He's has a really good article about saving old windows and why to do it.