Word blindness is an obsolete term for dyslexia, no longer used because the condition is a bit more complicated than simply being "blind" to what you're reading, but yes these two words have been used to describe the same deficiency.
Dyspraxia is a much "wider" term, i.e. it applies to "performing" in general and not just related to writing. What marks dyspraxia (in general) is that although you're not paralyzed and certainly not stupid you still have problems "programming" certain motor activities. It could be walking, or it could be related to articulation. Someone with dyspraxia who can't for the life of them imitate a shhhhh sound (this is just an example) will still not be able to do so if you instruct them to imagine they're blowing a candle out, but if you were to ask them to hold a lit match, they would (probably) be able to blow it out just before they burned themselves. So, no paralysis, just a difficulty with the planning and sequencing of motor activities. There are many different kinds of dyspraxia and for many different reasons. If you want to make it clear that you are referring to difficulties in writing, dysgraphia would be a more specific term.