@Jim Edward Walker The number is definitely achievable, It just depends on your plan and how you plan to execute it.
Because you have a 9-5 job, you will need to dedicate time outside of work to get mostly there, this means you will basically have a part-time job starting your Real Estate business, this is where I've seen many fail due to lack of discipline or not wanting to give up that playtime, treat it like a paid job. When I started investing I dedicated a minimum of 3 hours in the evenings on weekdays, and up to 8 hours on Saturday and Sunday, searching for deals, visiting properties, running the numbers, analyzing deals and neighborhoods, etc..
I would go to the local Home Depot in the morning before work and after work every few days, and on Saturday mornings to take pictures of the Contractor vans that had advertising/company Brands on them, then research them online, I did this to build a list on contractors that I would use to get quotes for rehab cost once I found a property.
In addition to getting on Wholesalers list, get on all of the public sites like HudHomestore, HomeSteps, Homepath, Redfin, etc.. and setup alerts on your phone so you get instant notification once something comes online.
Get practice analyzing the deals that come from Wholesalers, most of those deals will not pencil out with good profits but it will give you practice gathering Comps, pricing rehab cost on a project, etc. Do the same with properties on the MLS, most of these will definitely have little if any profit unless you're getting short sales, or old listings nearing expiration.
Depending on your financial situation, you may not have to purchase one property at a time to get to that 20 property target, You may be able to purchase Duplexes, Triplexes, Quads, or if you really have a decent down payment, a small multi-family property like a 6 unit building can be mixed into your portfolio to get you to that 20 unit target quicker, also you may get some deals that are more than $100 per unit in cash flow.
I see you're in Tennessee, I was in the Nashville area looking at properties late last year near Vanderbilt University, I didn't find any good deals but I was told I needed to get further outside of the Nashville area to get the deals. I only invest in heavily populated areas so I had to pass on the Tennessee suburbs.
That's the other thing, define your business model so you don't waste time in this process, the more you have planned the easier and faster things will go for you.
Good luck!