The discount is going to need to be at least what they could earn on that money in a simple investment.

Most likely it won't be up to standards and you are going to need to update/reno

I don't want to set the tone that I will come running for every little issue within 24 hours, but also want to just get these fixes over and done with.

If you were to need to sue, you would make all the costs you mentioned (lawyer, survey, etc) part of your claim as you would not have done any of those things if not for the fence being there.An additional option: after obtaining the letter from your township, municipal authority, etc supporting your position; survey results and anything else you have, give your neighbor a letter stating you are going to take down the fence he built on your property against your will.  

If she hasn’t been depreciating it but has been declaring the income you’re going to need an expert.

However the younger folks that I’m starting to rent to seem to be having less basic manners and skills and seem to need more reminders and guidance in being taught what is expected of them as they start living on their own.

Find a checklist online (either here on BP or a google search) and try to price out everything you're going to need before making an offer.

Based on the tone of your post, I would caution against getting too emotional.First and foremost, read your lease and understand her obligations and your obligations.If the tenant has promised to give you keys, wait. 

Do not expect them to "need" the work, they don't!

I am going to need to get a carpet cleaner in there, likely have a cleaning service come in for a day, and a few other small maintenance tasks.