Difference is your written English can be riddled with errors and people will still get it. As long as you have some knowledge of spoken English you can get your point across fine. The same is not true for character languages like Mandarin or Japanese.
Not sure what you mean, both missing strokes or having another character that looks or sounds similar should not impair the meaning of a sentence to most Hanzi user.
I can't compare it to Mandarin or Chinese, but as a non-native English speaker, I'd say it depends. Mixing up their/they're, lose/loose, fair/fare, cue/queue, etc, is understandable for me just fine. Having to know that "parody" sometimes means "parity" is when things start getting surreal.
