In this case, I will actually recommend to send from a shared IP address. Since you are starting with an empty database, your volumes will probably not reach 100.000 emails per month, being the very minimum you need to build and maintain a positive reputation.
There is nothing wrong with starting using a shared IP, and you will be able to migrate the account to a dedicated IP address once substantial volumes are reached. You don't need to migrate when reaching 100k, as volumes between 100k and 250k monthly are still acceptable on a shared IP.
When you need to migrate to the dedicated IP, you will need to do an IP warmup, as this comes with no existing reputation.