Nah I disagree. It's the best one. All of the extra shit other boards have just feels like needless bloat. Honestly the JS extension they added like 10 years ago is a bit much.
The site has an API for reading posts [0]. It works (worked?) quite well. For making posts, you'd need to write your own functionality that forwards the CAPTCHA and post timers.
No, you'll need servers and enough network capacity to handle the load, an understanding and supportive hosting provider, a law degree or enough money to pay somebody with one to keep you out of court/jail/prison, a network of degenerates to provide traffic and content and/or a copy of the existing 4chan content, a stomach of steel to deal with the content moderation duties, and a moral compass so warped you think hosting degrading and illegal content is "just liberalism and freedom of speech" and not something that needs a second thought by any right-minded person.
But sure, if you have all that and the source code, you're all set. Godspeed!
That's how it used to be (and the vast majority of early content is indeed lost). Most boards were auto-archived starting in the mid/late 2010s, though, with many archives being searchable. Some even allow ghost posting.