Welcome to self-managing rental units :) I'd be interested to know what quality of area this is in, A? B? C? D?
Between the rental units I own and the ones I manage through my property management company, there are almost always some things that pop up for the first month or two as tenants settle into a new space. Your tenants complaints don't seem too out of the ordinary. It seems like these small things all combined at once and noticed when they moved in is adding to their frustration.
I do this, and recommend you do going forward, is take a video walkthrough of the house between tenants including inside and outside of dishwashers, all appliances, floors rooms walls everything etc. If they say its dirty I would have them send me a picture and would compare it with my video walkthrough. If in fact the cleaner missed it, then you simply call the professional cleaner and have them come back to clean it. Blame it on the cleaner and have it corrected, easy
Mouse droppings is a valid concern. An exterminator is fairly inexpensive to hire and then you wouldn't have these tenants setting traps (correctly or potentially incorrectly) and not address the issue properly. You filled the spots you found with steel wool but there could be spots you missed and the problem could just get worse over time. I don't think plugging a few holes with steel wool and giving the tenants traps is the best that can be done. I'd bring in a pro.
The brown water is interesting, that I would have them send me a picture or video of prior to coming out to look at. If they say its intermittent, ok send me a pic when it happens again so I can show my plumber. If they can never send you a picture because its not happening then that puts and end to that issue quickly. Sometimes towns flush water hydrants or do work on main water lines. Usually this info is available on town websites or by calling town office. Could have been a bad timing coincidence
If a tenant wanted to bring in their own washer and dryer I'd be happy, no wear and tear on my items and no service calls when the washer doesn't work or the dryer doesn't dry. Most rentals in my area don't provide washers or dryers to tenants. Most have their own they bring with them from place to place. There is a big marketplace for used appliances so you can always sell them, I understand your concern about them sitting, the dryer could sit indefinitely and the washer would be the main item of concern that I'd just sell
Like others have said, you ultimately picked these tenants out of the 50 applicants you had. Use this to gain experience as to what you can do next time to avoid this, either on the tenant screening end or on the preparing the unit. I'd level set with them over a phone call or in person, not texting where there is no tone or inflection, that the issues they've brought up you've addressed immediately and lined up the people needed to fix and you want to have a good remainder of tenancy with them