Matt Risinger (austin-based homebuilder) did a freeze comparison between copper, pex, and sharkbite fittings some time back. It was pretty interesting.
At this point, I'd probably go for PEX-A (compression band) over PEX-B (the crimp style) because of the risk of getting the crimp not completely correct.
I used to work at a vertically-focused web search engine and ran the operational side of the crawler.
Also missing from this discussion would be a mechanism to rate limit (and determine adequate rate limits, based on your error rates) the crawl.
Also, detecting that you've been blocked and backing off so as not to further hammer the site you're crawling with requests. Related:
IP management is an issue here as well: lots of places just carte blanche block whole ranges from crawling activity. And will you be honoring robots.txt or not?
Be prepared for people to block you in new and stupid ways: once got blocked from hitting the site's name servers to even do lookups against them. They blackholed our packets. So what should have been a ~500ms DNS query at each http request turned into a 15s pause while the DNS request timed out ... eventually this stacked up across all threads, backing the overall crawling infrastructure to deadlock.
The Wayback Machine architecture is probably a good, public implementation of a large scale crawling mechanism. This post[1] about it may be a bit dated, but it's probably still accurate.
Probably the first thing to do is find a copy of Lawrence Chang's Handbook of Spoken Mathematics (also referenced in a previous HN post: https://news.ycombinator.com/item?id=10284052)
This has been great for helping me figure out what to even call various symbols so I can then go look up what they actually intend you to do.