Hi @linds_saun,
Thank you for your question about restoring your fire pit.
Your plan sounds extremely solid to me.
Unless the cracks give you a problem in terms of aesthetics, I don't think there's any need for you to repair them. There's a good chance that due to the heat associated with a fire pit, these cracks will reoccur. If you want to fix the cracks, you can use this Dingo 10KG Fire Rated Mortar.
If you empty out the pit and use a metal fire pit inside the brick structure, the majority of the direct heat will be contained by the metal fire pit. Having an air gap around this fire pit to the brick structure will further insulate against any potential damage to the bricks.
Sand with a high silica content as a base will certainly be beneficial to help dissipate any heat directed down into the ground. Alternatively, you could line the bottom of the pit with Scandia 1" Firebricks.
Overall, a solid plan that I'm sure will be fine.
Let me know if you have any further questions.
Jacob
