As you said, the answer to your question will largely depend on the number of visitors to your site. If you intend to promote the site heavily and expect it to grow rapidly, you may be best advised to look into dedicated hosting from the start, as this will save you the trouble of moving things when you outgrow shared hosting. However, if you aren't planning on becoming the next YouTube then your site should be OK here at DreamHost.
You can always try DreamHost for the 97 day money back guarantee period (be sure to pay by credit-card) to see if it suits your needs, but this would involve moving your content if it doesn't work out, which can be a pain.
These requirements won't be a problem, even on the Level 1 plan, but once again, it all depends on the number of visitors you expect.
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