Need advice on transferring files to iCloud - it's too slow

I'm looking to buy a new iMac or Mac mini and don't want to buy a larger drive. If I store all my files and photos onto the cloud, I shouldn't need more than 256 storage?

I am now trying to store all files into iCloud for the first time but I do have a lot of files. I enabled this in settings, but now it's taking too long. I started it last night but it doesn't seem to do much. See screenshot.

Is there a way to stop the iCloud transfer that seems to be doing all folders, and for me to pick and choose which folder to copy first?

I don't have access to ethernet and my wifi connection is great. Just need to understand if all of these files will ever transfer over?

Also, at what point will it prompt to pay for additional storage. I know I haven't signed up for this much data, so wonder if that's the problem?

Thank you in advance!