My retirement income is derived from preferred shares, exchange traded notes, and short term corporate notes. I do not own any common stocks, mutual funds, or ETFs. Here are my responses to your questions:
Do you stay away from issues that are not cumulative preferred?
No - most quality preferred stocks are non-cumulative. I buy only investment grade preferred stocks from banks, insurance companies, and REITs where I have a high degree of confidence that they will pay their dividends. I normally pick up new investment grade issues wholesale (below par) before they are listed when they trade OTC. You should also consider exchange traded notes. They pay interest rather than dividends but are senior to preferred shares. I do not own any rate-reset s or convertible preferred stocks and would not recommend buying them.
What sources beyond Quantum on Line are good to research issues?
http://www.dividendyieldhunter.com/
Preferred Stocks: Closing Table - Markets Data Center - WSJ.com
Bonds Home
Before buying preferred stock, bonds, or notes from a company, do research on the company itself. How much do they earn? Can they support their distributions? You need to asses their risk of default.
How do you find out which issues are "fenced in"?
Quantum online can provide details of all issues.
QuantumOnline.com Home Page
What are the mechanics of the purchase/sale process when an issue is thinly traded? (If I were to place a limit order how does a potential seller become aware of my bid?)
I always use limit orders on buying and selling. You should never use a market order. The bid /ask price and size are always provided with your quote.
What general Due Dilligence do you perform?
I check the rating, and research the company. Issues rated BBB- and above are highly unlikely to cause long term pain. For example I own JP Morgan preferred stock (rated BBB-) the likelihood of this company skipping payments is extremely low.
Keep in mind investment grade preferred stocks, exchange traded notes/debt, and bonds have outperformed the market in 2014, 2015, and so far in 2016. There are becoming expensive. Before buying any preferred stock, note, or bond, check for call protection. In this low rate environment, companies are calling higher coupon debt and refinancing with lower coupon debt.
I have been actively managing my money for the last 30 years. This is after I got burned by full service brokers in the early 80's and realized I needed to become more adept and investing my money. 98% fund managers, asset managers, so called wealth managers, and financial advisers are total losers who are only interested in lining their pockets.
Hope this helps