+1. A more detailed upload page would improve tagging by a lot.

URL checking: very helpful. Getting the best version can be tricky and most users have not read and mastered howto:sites and sources.

Smart source fields: very important. Ideally it would detect direct links only and prompt for a link to the actual submission.

Guided tagging: yes! Tag categories and clickable tags make things so much easier. I suggested something similar here: https://e621.net/forum/show/255964.

Pool/set/parent fields: I don't think this is critical but if its a common issue then sure.

SnowWolf said:
the more fields we put in here, the more simplistic people might get

I think you're right but it's still worth it. Some uploaders will start tagging less but most uploaders, especially new ones, will end up tagging more.