2) Pro/cons of single family vs duplex vs quadplex in these areas?

Yes, you are still protected as a single-member LLC... as long as you actually are a separate entity.

My wife and I currently have four single family rental properties, and are also interested in multi-family.

My parents own a 1031 Exchange, single tenant property and the lease is coming to an end.They purchased this property years ago and they have used it for their retirement income.They've asked me to handle the property for them and I'm not sure how to proceed.Does anyone have any experience renewals involving a 1031 exchange, single tenant property?

I'd bet a box of donuts that you'll have a logo for LAZ, SP+ (Standard + Central Parking), etc. on it.  

Single family homes can be had for 85-125k that generate 1100-1300 in rent .

For example, I know a guy that only buys multifamily, but comes across good single family deals all the time.I'm surprised by the people that turn to Wholesalers instead of realtors.  

First off you have to identify what kind of investing are you looking to do (single families, apartment complexes, etc.). 

I currently have 5 single family homes right now.

So check the median income per person, unemployment, single mother prevalence, racial diversity, vacant property rates and property and violent crime.