Avoid specific tools. There are so much SAP implementation in the world, someone has had the same problems you will encounter. So there is already a solution in SAP.
You will probably will ask for consultants (not probably, surely). Work with them for a standard solution for each issue, it is he key of future upgrades. You will upgrade.
Consultants know the product. You know your business. choose your best inside professionals, free them half their time, and promote them Key Users. make what is necessary for this to be a promotion.
And the first job of your key users is to choose the junior that will work their job the half tome they are key users.
By this way, after ending SAP implementation you will have a strong product carrying a strong team (normaly, the junior + the senior becomes an effectiveness duo, this is your personnal challenge)
this was for the human point of view.
for the technical side, converting your actual data to SAP database can be done with at least half a dozen of tools. Your job is to be able to export your data in flat files. Let consultants doing the insertion in SAP. The oldest technique is BCD, I continues to uses it dayli. It’s a way to simulate keying in sap screns in bath mode. The efficiency is based on the fact that loading is made with a batch input folder : you can track the errors and re-run data that are not already loaded. That is the key of loading SAP (or any other soft / database) : the warranty ofnever miossing any data.