The way you want to go sounds good but there are some small things to keep in mind:
ad 1. It is easier to export the data from the OVSD database directly. If you have an ODBC connection in place then you can import the needed data directly into Excel ad 3. Updating the data using Data Exchange works fine unless you want to clear some field values. E.g. you had a field 'Asset-ID' and now you want to clear it. In this case uploading the CI with an empty value for 'Asset-ID' will not clear the field value in OVSD. In these cases you have to either clear the value in all CIs using 'Update all' before the upload or you can make use of custom API programming using the web-api to handle this correctly.