Redoing Hearth - Want to lower it

My hearth had some ugly plain white tiles that I removed down to the concrete sub hearth. I will put new tiles over it or maybe a single slab piece but ideally I'd like to have the finished surface flush with the surrounding hardwood floor.

The concrete sub hearth currently sits just slightly above the floor level. From the basement I can see that the sub hearth is wedge shaped and one test hole told me even towards the edge it is more than 2-3 inches thick.

What I want to know is whether I would be opening up a can of worms if I just got Bull Dog Hammer Drill to try and take it down an inch or two. Then poured some self leveler to get my flat surface to put my hearth onto.

Other info that might be pertinent is that this is a 1908 house and I have no way of knowing whether this is original concrete or not. The area is 18 inches by 60 inches.

Otherwise, I understand I will need to use the self leveler anyway, and will want to make it as thin as possible so the hearth isn't raised up very high.

Do you think Bull Dogging it will be too much work? I would think the most work would be along the edge of the fireplace where I would need to probably use a grinder.

Any suggestions or tips would be much appreciated.

Ok, steps 2 and 3 are now done. I think I got a little lucky but also one of my fears came true. I used a roto hammer and found what I think was a seam about 2 inches down. My guess is that the hearth used to be brick and someone poured concrete on top of the old sub-hearth. So even though it was still a bit of grunt work, I could roto hammer along that seam and get a number of large chunks to come up.

My fear was causing some secondary damage from the impact and vibration of the roto hammer. I was also concerned about where the subhearth connected to concrete beneath stove and brick surround. Sure enough I got some damage on the concrete floor of fireplace beside the stove that I will have to patch. Sorry I don't have photos, so hopefully that's clear.

I did not find any rubble but maybe that is a bit further down. So following getting it all to about 1.75 - 2 inches below floor, I poured a thin layer of concrete prior to using the self leveller. In hindsight, I should have used cement or maybe build it up a bit higher. There are a couple of high spots where cement does not work because you end up with gravel and no binder.

So the next step is to pour about a half inch of self leveller over concrete. But I'm concerned about getting this right so in the end my tile is flush with floor. The area is small, only 18" x 68", but if the floor is not level, and I use self leveler, then it won't match from one end to the other.

I also don't know how much to account for the thickness of the thinset. If I use a 1/4" trowel at an angle, I'll get maybe 1.8" of thinset thickness, but then doesn't that compress a little bit once the marble tile is set into it? Any experienced tilers out there? I've heard cardboard thickness used as a rule of thumb, which is probably about 1/8".