How well do relays handle actually long articles? I had tried to copy-paste content from Wikipedia and those more often than not failed to save and I guess it was a size limit thing.

For me, a size limit can also have its good side especially in the context of a decentralized wiki but it should be explicit and not just throw away what I wrote.

Imagine a reasonable limit driving articles into composable sub-articles that can be included in the main article much like kind-1 notes get embedded in each other. 

 Foaf model helps. Tier 1 and 2 npubs have a much higher bytesize limit for us