If you disable the clustered index, the entire table is inaccessible (can't be read or modified), so you can't do that before a load or the load will fail.
As for disable NC indexes before and enable afterwards, maybe. There's no hard answer that works everywhere. It depends on the overhead the indexes would put on the insert and on how long it takes to rebuild them. You have to test and see what works in your situation
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability