and believing that Joe/Jane Home Buyer buys a home based on what they can afford monthly" You can bet on that.

So I don't bet on appreciation, but on that side of 108, that's probably where most of your money can be made.I know much less about Exeter, but from what I gather talking to people, it's in the same boat as Dover for all those points I made above, only on a smaller scale.

House hacking may not be an option since you mentioned you have young kids which means you will be looking for better schools and there may not be tons of multi-family options in those neighborhoods.A few other options:  In lieu of taking a loan on the 401k , limit those contributions to get the employer match, or stop contributing altogether. 

***Only exception is if an owner has plan & funds to reposition Class D to Class C or higher.https://www.biggerpockets.com/forums/776/topics/960183-what-they-dont-tell-you-about-cheap-rental-properties?

possibly but I am willing to bet on the long term outlook

It's either a) work hard b) manage it c) or manage your manager.

Never BET on appreciation.

A 4-plex in Class C or D area (Compton, Watts, North Long Beach, etc.) will have a higher cost due to common late or no rent payments, evictions, etc.

Its more expensive but getting a good tenant is gold despite having a spreadsheet with good returns coming back at your for class C or D garbage.

At best you put 40k into that 20k property and you have something that looks like it belongs in a C or B neighborhood, with half the price, 1.5x the rents and the tax burden is 1/6th of what you have in those areas.