I've never had an issue with wearing tights over cycling shorts. My shorts don't have drawstrings and if tights come with one, I pull it out, if they are tight enough without it. Maybe I am just used to that "tight" feeling?
As far as the leg warmers go, I can only wear mine with my Terry Bella shorts. The high amount of lycra holds them up well and the shorts are longer than my Shebeest S Pros. I also bought leg warmers that are for women, that come in actual sizes, from Sheila Moon. That's what really helped.