How to tile a fireplace hearth?

NSuzette

Hello

I'm a newbie renovator /interior designer and I want to tile this fireplace. My specific questions are;

1. How should I go about levelling/preparing it all? The bricks (concrete I think) sit about 25mm proud from the surrounding floorboards - how should I try to build up the surrounding? (It was recommended not to remove the bricks as it was unsure what, if anything was underneath). Should I try to fill in all the holes and dents on the bricks or should I put some backing board down to level it (or both)?

2. What substrate should I put under the tiles, if any?

3. What would be the best way to fill in the 'letterbox' opening in the brick wall behind the hearth, or should I just put a board/some sort of substrate over it and tile onto that?

Feel free to send any 'how to' links if you have any - especially good 'how to tile' utubes!

Fireplace (showing the 'letterbox' hold in the bricksThe bricks sit 25mm proud of the floorboards