The market went crazy for almost a decade. 

I did this personally for about a decade and my business partner who I did it with has done it all his life 3rd generation logger.there is huge money to be made in Timber if you know what your doing.  

A lot more than my PITI costs combined.The condo charges a $250 sublet fee for renting out my unit; That would bring my total monthly expense over $2600; Based on what I researched I could get for rents in this area, not sure I can get $2600; Even if I could I would just be breaking even with no cash flow; Wont include amount needed for potential vacancy; The sublet fee kills my flexibilityDecision - Sell CondoProsWould probably get top dollar on sale of home selling now; if there is a downturn it can be MANY years before I can get the money I would be able to get now (anticipate $425k to $450k)Sell and use part of the money to buy new home for myself and/or use the money on alternate investment(s)Keep the money liquid for opportunities that come up in the next 1 to 2 yearsFree myself from the politics of the condo board and how the complex operates; A lot of the issues are financial in that over the years money has been collected and not well managed or spent which is why HOA fee is so high; this provides a level of inflexibility on managing expenses which I have limited control overConsDon’t have that much left on mortgage; selling now would mean investing elsewhere via new long term mortgage at todays higher interest rates (albeit at smaller mortgage amt since I would be able to put down a larger down pymt); Additionally, at todays market prices, I would not be able to get a unit like this one for the price I paid over 2 decades ago and for the interest rate I have nowI have been wanting to build a real-estate portfolio and my thought has been that this would be my 1st unit in that portfolio and I should keep it & build from there; Selling would mean starting from scratch instead of building; However is this Condo Unit really a good investment? 

It depends on the area but in most places it will be north of a decade. 

Been managing 15+ units under my families residential properties for almost a decade now.

I'm a buy-and-hold investor and I'm planning on holding on the property for decades, so instead of immediate resale value (which ADU doesn't compare very well with perhaps other rehab/flip projects), I care much more about long-term cash flow and long-term resale value.

I've vacationed in STRs for decades.

To make it worse, if it's a condo conversion you could hold it for a decade and then decide to do a condo conversion... it's short-term capital gains as you only owned the condos for under a year...that hit me hard...3.

I've partnered with developers who have decades more experience than me, and they still run into this. 

As long as the quality of the tenants are available to the location of the investment, you were certainly able to capture the profit from the Amortization of a fixed Rate Mortgage.Over the decades, my pro-forma models have proved this to be a very compelling reason and time has proven it to be both accurate and profitable.This Exercise will teach you a lot about Investing in General and you will have a huge advantage over someone that only knows a single way of analyzing just one specific investment or using one specific calculation.Continue the good work!