Someone recommended that I add 12-18 inches of 1/8 inch shock cord to the tarp at the tie out points to provide some flex in strong winds. Is that common practice?

Also recommended was #18 braided nylon Masons twine for guylines because they're not as susceptible to tangles when stuffed in a sack. That would be advantageous for me in colder weather, as I quickly lose my fingers when carefully coiling half a dozen guylines. I have been using the 1.75mm single braid dyneema sold at Warbonnet.