Here are some tricks you can try with pick slides. Think about this, the E,A,and D strings are all different guages. Therefore, the winding on the strings is either smaller or larger, kinda like different coarseness of a file. With that in mind, try your pick sliding on these different strings. Each will produce a very different sound. You can also get a type of slide sound on the first three strings. This will take some practice to get used to. You can also use your hands in an up and down crossover pattern that sounds really cool. Also bear in mind that the speed at which you drag the pick down the strings alters the sound as well.

As for you other question. I'm not quite sure about what you mean there, but try this. First pick the note and then lightly touch the string of the picked note at an interval of an octave. You'll get a good harmonic out of there. You can also fret the note and find alternate harmonics as if you were using a capo.

Give those a try and have some fun with it.
Good luck.

JAM