4) In terms of submitted content I am aware that not everyone is fully fluent in English. If the article makes sense to me, has an idea or two then I do not worry if the article is a little 'off' in terms of grammar or usage. I also consider the context. If an article is, for example, written by an Indian writer for an Indian audience then I let stuff slide that I'd not do for a writer, Indian or not, aiming at a US audience. We rank pretty well in India. ;)
However you need to take a judgment see more for the overall quality of your site. This is not always an easy balance to reach.

5) If you have good quality content post it to your own site first. Then, for best results, rewrite it for submission elsewhere. There are tools to help you with rewriting but if your own English is at all dodgy then be careful in using them as they can, unless you know what you are doing produce some real rubbish output. I use two tools for my rewriting, you can Google for them based upon the names: "Content Composer" and "Rewrite Rocket" both from the same stable but taking a different approach to the task. Rewrite Rocket is the faster and easier to use of the two, it is also cheaper.