What happens if my accounts go over the limits for my plan?
It depends on your plan. The free personal plans get restricted for one month in most cases or permanently suspended if deliberately is creating issues and the information in the offending libraries is removed. The paid plans have priced tears that are applied/billed once a month or yearly or both depending on the case.
How can I transfer files to China Mainland?
You need to have a multiuser plan and user https://nihaoconsult.com or https://app.nihaoconsult.cn
Here is a short article about it: https://nihaocloud.zendesk.com/hc/en-us/articles/360021015773-How-to-Share-Files-to-Mainland-China-Users-