"(How) Can I place the same symbol (Z as an example) on two well separated lines in TWS? Buy orders on one,Sells on another.Or market buy/sells on one and trails/stops/limits on another.Can this be done with all the various orders under the 'one cancels all' umbrella?"
This is how I do something similar to what you are looking for.
Type in the symbol you want lets say for example IBM.
Then click on the ask price as many times as you like, each time you click on it it brings up another buy order line. Then to make changes to these lines do any or all of the following. If you want to change one of the buy orders to a sell order click in the buy box and select the sell option. If you want to change the limit order to a market order or any thing else then click on the limit box and select what ever you want.
Hope thats what you were looking for.