This is a great place to learn and to connect with people so take advantage of all the great resources.

Your biggest risk if you execute the plan will be running out of money in retirement, either due to natural longevity and/or later health issues draining your resources.  

Sell them and put a down payment on something bigger? 

. :)    I HIGHLY recommend you Talk to Engelo he is from Aussie land and is quite famous on the Aussie version of Bigger Pockets thats how I met him in 2012 or so.. he has been investing and rehabbing in US for 12 years now very successful at it and a NO BS kind of guy..

Susceptible to all of the items listed above, plus snake oil schemes, and outright frauds.Also, the "Double-Downer" - They DO get started, but once started, can't stop, and just continuously raise more and more money, for ever increasing "doors", and bigger, and different deals.

It is very easy to do. 75% of my real estate brokerage clients are people who have exchanged in or out of a different asset to make their lives better - more units, bigger buildings, newer buildings, better location etc...1031 is the way to go with a solid real estate team. 

A Pro membership gives you the tools and resources you need to start, scale or manage your portfolio.

Absolutely, you can use a 1031 exchange to delay paying taxes when selling your 4-plexes and buying a bigger multi-family property with an LLC, even if it's just you in the LLC.

Happy to connect and share resources in the area. 

I'm happy to connect and be a resource.