Even for a serious site I think it's a decent starting point, obviously it will need to grow much for the website to be considered successful

What's yor number BTW?
First of all, its very hard to define and track real "traffic". What is traffic? Unique visitors? Refreshes? Time visitors spends on page? Number of pages visitors click? What is more relevant as "traffic" statistic - 4 unique visitors who will left site after 5 secs or 1 unique visitor who will stay on site for 4 hours, and will have high click through rate? There are many tools, some are very expensive, which tries to measure relevant traffic. But lets stay on Unique visitors for now.
333 UV/day is good for start but cant be considered high. For example, news portal I visit has more then 300.000 UVs/day, and tech portal more then 36.000 Uvs/day. Both are non english, with limited audience of small country.
About successful site - it depends more on "quality" of traffic then on "quantity". For example, I have a minisite which receives about 200-400 UV/day, but generates less revenue then my other (parked) page which receives 30 UV/day but has 60-70% CTR.
One part of my (adult) network of sites receives almost 30.000uv per day, and I wouldn't call it very successful. On the other hand, If I would have 30.000uv/day targeted traffic on real estate site, I would call that VERY successful.
My point is - quality of traffic is hard stuff to measure
