I’m a 300/500 partner, I’ve had to do this before.

You don’t have to repurchase any modules. You can have as many companies as your hardware can handle. You want to activate DI and DP so you can import into Staging tables using Assisted Company Setup and data entry screen where appropriate. Do a test. Make a copy on your database and register with your test license. Go into company maintenance and add a new company. Log into it and start running through the tasks in Assisted Company Setup. But you REALLY should be using your 500 partner for this, I can’t emphasize that enough. Even a better way, because the data is already in SQL  in 300 would be to back and restore the 300 data db to the same server , setup a linked server and use the APIs to pull the data into the 500 staging tables. Either way, don’t do anything in your 500 production database and I recommend using a partner to assist. If you want to do the lions share of the work that’s great, but there’s no substitute for experience.

I really appreciate your assistance. I will heed your warnings and will definitely only work in my test database. I am a developer and am very familiar with the tables and API. I wanted some feedback to make sure I was on the correct path. I definitely will be talking to our partner if things go sideways. For right now we are just throwing around the idea.

Thanks again. I hope you'll be around to answer a few more questions down the road!

I really appreciate your assistance. I will heed your warnings and will definitely only work in my test database. I am a developer and am very familiar with the tables and API. I wanted some feedback to make sure I was on the correct path. I definitely will be talking to our partner if things go sideways. For right now we are just throwing around the idea.

Thanks again. I hope you'll be around to answer a few more questions down the road!