Thinking to migrate from sage to Odoo. Really,it is good option to manage all aspects of your business. There is a procedure for migration process in which you have to export all your information from SAGE into a CSV file. You can then change or add column headers so that openERP/Odoo automatically knows what column to put the data in. Each data type needs to be put in separate CSVs.
For instance - you cannot import partners and sales orders at the same time. you need to upload the partners, then map the ID created in openERP/Odoo to the partner field in openERP to the sales order CSV you are uploading.
This is pretty simple, but it is not an instant process, you should take some time to learn exactly what the columns in openERP do. Don't assume a column name means what you think it means or that SAGE will export all the columns you need to get your data into openERP seemlessly. Like if you have accounting installed, you must import the partners with the proper AR and AP accounts, or you will be prompted to add that information manually later.
Another option is to use the CSV files, and read them by script. Than you can do additional checking/modifying. And you do not have to edit the CSV-file for the orders, use the ID of SAGE to search the user (have to add a field, like sage_id, to res.partner though).
Many Odoo partners also offer migration services. It might be worth your time to get a quote from some experienced in migration.
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