You will have actions to take if any of these affect your business
1. Employment : if you employ people this will change and also if you currently employ EEA citizens this changes in June 2021 ( more details when available).
2. Import or Export especially if you trade with NI: get a EORI number now.
3. Pay Tax and have a EU Subsidiary : because we are moving from EU jurisdiction Double taxation rules will change
4. Transfer data to and from EEA: if there is no deal transfers from EEA may cease until a deal is reached, watch if there is a deal and there is no adequacy agreement, again you may need to appoint a data controller in EEA.
5. Visas: you will need one if you don't have a EEA passport, that will be set up shortly in 2021, and it will not be possible to spend more than 90 days in the schengen region in any year.
6. Sell in EEA : may need to register for VAT in that country and also appoint a fiscal representative, It may be too late to appoint a fiscal representative for January . Complete customs documentation.
7. Import from EEA: how you complete the VAT return will change.
8. Move goods from NI to GB: apply for an extra EORI called a EORI XI
9. Move goods GB to NI: you will need to complete customs documentation.
TAKE ACTION NOW....