Muriatic acid is hydrochloric acid and I use it regularly to clean stains off the toilets 
or remove rust from metal.  It will eat concrete and is used to clean stonework 
and etch concrete -- as you are planning.

Although I laugh at those who worry about oxalic acid powder, I will warn anyone 
using this stuff to be careful.

Don't breathe it -- the fumes can be overpowering -- and don't get it in your eyes.  
It will do instant damage.

As for exposure on unbroken skin, if it is washed off fairly quickly, no harm is done.

Keep lots of clean fresh water and baking soda around to deal with any spills or 
splashes.

As for preparing concrete for finishing, I would call the local rent-all and ask about 
concrete grinders and polishers or even call a local concrete finisher.  A power grinder 
will polish off the imperfections, and if the water does not run to your drains just right, 
any bumps can be taken down easily.  If any chips and gouges are filled in advance 
of polishing, the floor will be like new.

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