All walls eventually fail! It is much better to slope ground to the
angle of natural repose. That means it will naturally not fall over or
move.

Your wall building idea sounds fine BUT one day you or someone else
will have to rebuild it.

just as you are removing that old wall thats falling down.

just something to think about.

After rebuilding some walls repeatedly I have removed 60 feet or so of
them and have never regretted it. Have plans to remove another 40 feet
or so the next time it begins to fail.

I will have to retain about 10 feet of wall, thats about 10 feet tall.
Since 1972 its been rebuilt 3 times last rebuilt made it 2 heights
that helped a lot.

install gravel and perforated drain pipe behind wall, freeze thaw of
water causes much wall moving.

incidently dry stacked solid concrete wall stones are easier to rebuild
than ones concreted in.

sadly all walls fail sooner or later

I have lived in my home since 1972.