Ahemm.. If you want to generate customer ledger records, GL entries and tax entries from the sales orders, then your best bet would probably be to use the F47 or Z-tables and roll your own post-processor to update the imported orders with invoice number, type, company and invoice date and then let sales update take care of the customer ledger/financial records and closing of the order to status "999". However, the financial posting period needs to be open so if you're importing historical orders from years back, you would need to have the oldest period open for A/R and G/L entries
If you do not need to get the customer ledger or G/L entries then your post processing UBE just needs to set the next status to "999" and G/L date to invoice date and the run R42996 to move the records from F4211/F4201 to F42119/F42019
Also, if these are stock orders, you would need to set the related P4210 processing options to not check availability and also (in your post processing UBE) set the actual ship date and set on-hand updated (SDSO02) flag to "1". I always favor migrating old sales orders using a non-stock line type just to avoid any integrity issues / false negatives between F4211/F4111/F41021/F41112 and F4115 but you approach could be different based on the requirements
1) Populate F47011/F47012 and run R47011 to get them into F4211 at status 980/999. (setup as you advised)
2) Custom UBE to re-read from F47012 and update F4211 with fields that aren't populated etc.
3) Use R42996 to move them into F42019/F42119.