do I need an EORI number to register in the EU information system

Yes, and that mainly comes together at customs

An EORI number and registration in the EU information system for the deforestation regulation are two different things, but they intersect at an important point: at import or export. The EORI number is your identification number at customs, required for every declaration that crosses the EU border. Registration in the EU information system is a separate process: in it, you establish who you are as a market participant or trader under the deforestation regulation, and from that follows the due diligence declaration that belongs to a consignment. Both numbers exist alongside each other, and at import or export they come together in practice because customs places the information from the declaration alongside the customs declaration.

For those who trade only within the EU, without a product crossing the border with a third country, the EORI number plays no role in this process; registration and the declaration remain necessary, the EORI number does not. As soon as import or export occurs, the connection becomes concrete: the reference number you receive after submitting a declaration must be linkable to the customs declaration, and that link runs through the information customs already has about you, including your EORI number. How that link between declaration and customs declaration works exactly is described on the page about how the due diligence declaration number relates to the customs declaration. Those who do not wish to carry out registration and submission themselves can also outsource it; what that entails is set out on the page about authorising a service provider to submit a due diligence declaration.

Where this follows from: the EU information system and the customs link

The EU information system for the deforestation regulation, the due diligence register, is the place where market participants and traders register and submit declarations; its structure and operation are explained on the European Commission's page on the implementation of the regulation. The fact that this system stands apart from but must connect to the customs processes at import and export follows from the way the register is set up: the reference and declaration data are intended to be consulted by customs when making the declaration, which makes EORI registration relevant once a consignment crosses the EU border.