The TLP TC (not plugin) is fully responsive, so if you reduce the space by having sidebars, the columns automatically decrease in number (simply decrease the size of the browser to test this), see Pavilion
See the Layouts plugin to add customisable sidebars. Read more about that: Pavilion
Alternatively try Fakebook TC, which is one column all of the time and has some inbuilt sidebars.
topic list excerpt has some issues for all implementations because the serializer is sending a lot of unnecessary junk (e.g. including the onebox anchors!) … this can be styled out to some extent - just did it on rideables.
This is native, just included within TLP’s output.