I'm the creator of searcha.page and seek.ninja, those are the basis of my index. The biggest problem with ONLY using that is freshness. I've started my own crawling too, but for sure common crawl will backfill a TON of good pages. It's priceless and I would say common crawl should be any search engines starting point. I have 2 billion pages from common crawl! There were a lot more but I had to scrub them out due to resources. My native crawling is much more targeted and I'd be lucky to pull 100k but as long as my heuristics for choosing the right targets it will be very high value pulls.

Most likely it is, the issue then becomes being able to store and afford the storage for all the files.