Regarding point 1), I have experimented, with myself and with some of my athletes, including Lactate Threshold work in the long runs. I usually do it in one block, like 20 to 40 minutes at LT pace within a 90 minute run, for example (could be something like 50+ 30 LT +10).
I have had good results with this but I will try to split it into shorter intervals and see how it goes.