What happens if my accounts go over the limits for my plan?
It depends on your plan. The free personal plans get permanently suspended and the information in the offending libraries is removed. The paid plans are negotiated on a case basis, you will be contacted by Customer service on this regard.
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-