Good afternoon Michael!
Well I must disclose I am somewhat impartial to the property management business as I own one, however I do not manage anywhere near Baltimore, so I feel this advice will be fair and unbiased. Though I always strive for that, we all have natural biases when we have skin in the game. I hope my experience managing 900 rentals will prove to be of value to you.
To answer your initially question about the safest way to set up self-assisted showings, I'm not sure there is one. The best resource I have seen is Rently. It is a lockbox that is placed on the front door and prospective tenants can enter their credit card info into Rently customer service, get a hold placed on their account, and view the home. There are a few problems here however:
1. I have never priced this, but I heard Rently is very costly to roll out, and may never make sense for a small portfolio.
2. I still can't wrap my head around the insane amount of liability on your head when a prospect whom has never been vetted in any way shape or form views your home unassisted. From damages to the home, to potential injury to the prospect, the risk-adverse side of me cringes at this idea.
But it's an option...
I think your best route will be to hire a good, high quality, high protein property management company. I will say this, there aren't many of us out there, and you cannot interview enough. Interview, research, interview, research, rinse, repeat. A bad property manager will cause more destruction than you can imagine, however a good one will ALWAYS make you more in the end.
My major factors that matter most in hiring a good PM:
1. Communication: How do they funnel rental leads, manage incoming calls, etc. What are their hours of operation? We are open 8-7 monday-friday and 8-5 on Saturday. You can call us anytime during those hours and you will reach us with ease. Most PM companies however you have to jump through 14 different hoops then you're stuck with a voicemail and never get a returned call. This is by far the biggest point to hire by in the PM world.
2. Reviews: If a PM company sucks, it wont be hard to find that out by a quick google search. We have a 4.5 rating on google with 59 reviews. We are also on virtually every other website available with positive reviews across the board. We aren't perfect, and so many prospective clients ask about the negative reviews online to which I give a good explanation for. But nothing tells a company more than their online presence. If they have no or little reviews, they are either a mom and pop or aren't experienced. If they have a bad google rating, you don't want them. You want the company with overall good reviews and plenty samples to choose from.
Notice what isn't in my top things to hire a PM? Price. Of course that is important, but quality, excellence, and a track record of success are top priority.
Let me know how else I can help!