It all depends on your cpu usage, if you are just serving some static html with some files (flash in your case) it shouldnt be an issue.
20GB a day makes 600GB a month. This is clearly within the 1TB limit (this will grow ofcourse).
If you are using a content management system or advanced scripts it might become a problem.
BTW 1: most content management systems have caching options to reduce cpu load.
BTW 2: you could consider the Code Monster Plan too make sure you will not hit the limits.
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