Yes, all you're doing is upgrading your hosting plan. As long as your new plan includes one free domain (and all hosting plans do), you'll continue to get the free renewal every year.
Did you mean accumulated growth? In either case, we haven't gotten reports of exactly what happens to your limits when you upgrade your plan.
Well, the dedicated server plan limits are 500gb disk storage and 5TB bandwidth (same as the Strictly Business plan). Is there some specific question you had about upgrading to a dedicated server?
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