I wish you luck and I hope you succeed, but you make it sound much much easier than what it would be.
First of all, you're going to drown in hardware costs, if you run your own hardware. If you run on AWS, you will be the largest AWS customer. 2 years ago, when Google was still displaying result counts, I got 1.3 billions results for "sushi"[1]. This means that if you use a reverse index to lookup your results, the "sushi" entry will be ~19GiB large, assuming you use UUIDs. If you think 90% of this is spam, and you only index the non spam (detecting spam/seo is far from trivial, but let's say you figure it out), you still need ~2GiB just for mapping "sushi". With 755,865 words in the English dictionary, according to wikipedia[2], you'll need ~1.5 PiB (yes, pebi/peta, 1,536 TiB) just to store relationships for English pages. This is assuming you don't support other languages, you discard 90% of pages, and you don't cache the content of pages for re-indexing.
In addition to this, you also need to store the meta-data for each pages (vote counts from your voting system, whether it's serving different content, etc...). The order of magnitude has to be in the O(100TiB) from my conservative gut feeling. (still assuming you discard 90% of the web, and I'll assume you aggregate the metadata on the domain, not on the individual pages)
The second challenge is your ranking. Now that you've become the dominant search engine with your awesome ranking system, you will become the main target for swaths of motivated click-farms which are exploiting workers from low income countries. They will be trying to register accounts, vote and game your ranking. You can most likely detect this behaviour, but their behaviour will be very similar to a significant portion of your real users. So you'll be fishing in a pond with a rocket launcher, and some of your legitimate users will be collateral victims. Otherwise, you'll spend most of your time playing a cat-and-mouse game with the SEO spammers instead of improving your search engine and fixing bugs.
I'm also falling in the trap "i could rewrite that in a weekend" sometimes, but for a search engine, I would love to see decent competition, but it's near impossible.
[1] https://news.ycombinator.com/item?id=30925402
[2] https://en.wikipedia.org/w/index.php?title=List_of_dictionar...