Think about some small, healthy ways you can reward yourself when you complete different stage of the project. Perhaps you can sit down and enjoy a movie or have a nice meal.
Be compassionate towards yourself, remember that you made the best choices you could in the past with the information and resources you had at that time.
Try not to be too self-critical when you come across things that you wish you had dealt with years ago or wish you had never bought in the first place.
Recognise that you may need some emotional and practical help as you undertake this work. Think about where you can get this support and who you can reach out to.