Data Uploading Process:
1. Master data (GL accounts, customers, vendors, assets, cost elements, cost centers, profit centers etc.)
2. Transactional Data (Open Items for customers and vendors, GL line items, Cost Center planning, profit center plan data load etc.)
In the first case mostly you can use LSMW, if you are conversant. The following document is useful to you.
Note: No template is suitable for you, because, your configuration is different and their configuration is different, field status of various fields must be different. Therefore, follow the above document and start from fresh with recording. Recording is more or less sufficient for master data.
In the second case, you create 5 Offsetting accounts + one main offsetting account.
1. Vendor Offsetting Account
2. Customer Offsetting Account
3. Asset Offsetting Account
4. GL Offsetting Account
5. Stock Offsetting Account
At the end of the day, the total balances within these accounts must be ZERO. Make ZERO these accounts and transfer the balance to MAIN offsetting account. Once you have done this, make sure you have blocked all these accounts.
Technically, in second case, you should take help from ABAPer to write BDC, particularly in case if your entries are having different line items. For example your first document is having 5 line items and second document is having 10 line items, in such case LSMW recording will not work. You can depend on some standard SAP programs to map the LSMW. If you are not conversant with how to map, then you can refer the following document posted by Naimesh.
Still, if you are not able to map, then there is no other way, you need to depend on ABAPer for uploading the transaction data through BDC. He / she will create a program and a customized transaction code for you and provide you the format. You may have to help the ABAPer with your requirement what you are exactly looking to upload.