Ron,
Your concern over the market, economy and property conditions are all extremely valid concerns and any investor not taking those into consideration are likely not going to last as real estate investors.
As James stated, I would not buy a single family home right now. Oil job losses are going to affect that market most significantly. We are already beginning to see that happen. Many home owners are putting their home on the market, even if they didn't lose their job, out of fear of the economy. This typically leads to this market being oversold and will soften home valuations in the near term. The same thing happens in the stock market, people overreact to negative news and sell off over fear. This is why you see the stock market have such high losses and gains over short periods of time.
I also recommend staying away from condos if a primary concern of yours is liquidity. Condo associations are subject to unique issues that other properties are not. They can lose government financing if the association is mismanaged or their are too many tenants (for example, FHA loans require an association to be 51% owner occupied throughout the association). Also, certain condos have rules on using it as a rental (to avoid losing financing and other reasons). They can be good investments, but it depends on your goals and strategy.
I highly recommend a multifamily property. 2-4 unit properties have gone up significantly in value in recent years, however, as long as the property still cash flows, it can still make for a great investment. Interest rates on loans have never been lower, which is offsetting the rising prices. Duplex properties cash flow way less and often don't do much more than break even when fully rented if using owner occupied loans (FHA, VA, 5-10% conventional) where 3-4 unit properties cash flow at a much better rate. The 3-4 unit properties sell very quickly, if they even reach the market. Many of my clients are able to buy these properties before they hit the market because we are made aware of them before MLS or they get the information right when it comes to market.
Sounds like you have a good idea of what your goals are, but need a better idea on the path and plan to get there. I will message you to discuss further.
Jon