If there is blood, I still believe it's ILT, but no matter--you really want to start with healthy birds and I wish you the best in your new chicken-keeping career.
You can certainly use bleach, though if I was battling something like ILT, I'd use Oxine,which kills far more than bleach does. There are also others made for this like TekTrol. I'm no expert on ILT so I"m not sure how long you'd need to wait before you get more hens. I'm sure someone will know...
Look up ILT which is Larygotracheitis, a serious illness. The blood is from a tracheal hemmorrage. Those will be carriers for life if this is what I suspect. Sadly, I would cull all of them then disinfect everything and dont get more birds just yet. Antibiotics will not keep them from being...
In my opinion, coughing is much worse than sneezing. Sneezing is often environmental. I have never in my life heard a chicken cough. If I did, I would probably euthanize it. If you get antibiotics, you are treating it blindly and it may be viral and not treatable with antibiotics. The hardest...