By that time everyone is aware of what other "comps" are going for (reminder that buyers don't care about how much you spent on XYZ, they see similar-ish homes and that's their benchmark). 

My plan was to do something very similar and use the cash out for new property down payments.

Prices in those segments have seen upward pressure, similar to trends in other rapidly growing areas.

I actually worked with a client in Phoenix not too long ago who was in a similar boat...trying to transfer their loan to a buyer looking to use the property as a primary residence.

Depending on which brokerage you use, you could possibly borrower against your securities holdings with a line of credit (similar to a margin loan) if it's not a retirement account. 30-35% of the balance would likely be within reach, but make sure you FULLY understand margin calls and when they would trigger.

Similarly, if you put all Class D tenants in a Class A 4-plex, what do you think will happen?

There’s likely a carrier that’s most aggressive in the city where your 4 unit is located and comparing your premium to that of similar properties  nearby will be the most accurate assessment and point you in the direction of the most aggressive carrier.

The main thing to me has always been to respond honestly, try to avoid being negative or (worse) calling the customer names, and similar.

I want to increase my personal income to help fund a second rental, but my career limits me mainly to remote jobs and gigs.I’m curious if there are any other investors out there that started with a similar skill set to mine, and what other skills they developed to help increase their W2 income and to help build their real estate knowledge and experience? 

As you know, there are other communities that behave like investor clubs/networking groups that present themselves as educational platforms, yet they are either operated by deal sponsors/syndicators or have a number of deal sponsors/syndicators that sponsor the website (they may not call them sponsors but preferred vendors or similar).