Whats the best way to know if your startup is ready? build a prototype, get some traction, look at the numbers, measure, experiment then measure again. If you truly are going to scale (and you are growing at 1% a day) and you've experimented enough that you've found a suitable path you'll end up needing money of the VC scale.
It doesn't cost much to sit around and build something. Go and test it - figure out what people want first - change your assumptions and above all PROVE that if you scaled your site it'd be worth it for investors. You don't need VC yet to start something and test it out - If it comes to that point well thats something to think about.
I'm reminded of the story Michael Birch of Bebo tells - they built something, put it out there off the traffic of birthday alarm and experimented with features. Every time a feature added to the growth of the site and got a noticeable increase in users they kept it and tried something else which also contributed to the growth. By experimenting, measuring and then iterating for things which correlated for growth they ended up on the right path. When they had 5 million users and were growing month on month they had the numbers to prove themselves. They took $15m from Benchmark capital. The bottom line - you'll know when you are ready: just go prove the numbers.
Almost all sufficiently large startups eventually require Venture Capitalists. So there is no hard and fast rule on this; just take the money when it makes sense.
The real principle here is the golden rule of spending money- no matter what the source is: put yourself in the investor's shoes (even if there isn't one). Pretend it's your $10,000 or $5mil and you're investing in a company that you have little control over- would you be pleased with how it is spent?