BigmouthinDC is right on with his response. There are technical reasons for why this is all true, but the simple answer is, you are all good. Here are a few fine points though:
1)You want to place the stud wall at least 1" from the concrete slab but try to avoid making the total air gap larger than 6-8" if possible. Ted and I have talked about this numerous times and I only sort of understand it (I suspect this is a convention and the reasons why are a little more based on experience than science), but he suggests you drywall the ceiling between the stud wall and concrete if you start getting a really large gap. I have a 2 foot gap in an area and had to add 5/8" drywall to ensure good soundproofing. I believe its thought to be a flanking source. You mention rigid insulation, if so, make sure the studwall bays are still filled with fluffy insulation.
2)I think Pink is better. The kind of testing we need to draw solid conclusions simply doesn't exist, but it is my belief that the lower density insulation would be better in the wall. It's important to fill the space but it should be treated like the inside of a speaker enclosure in some ways. it doesn't need to be 100% covered like its creating an airtight space. You want the majority of the bay filled loosely. It should not be packed in tight and you want to avoid, if possible touching the wall. The last part I think would be interesting to study, but as I understand it, the lab tests were done without insulation touching the drywall so if we want to equal those results, we want to avoid making changes in our design. The cost of cheap insulation is so far below that of Safe N' Sound that I think its silly to do anything else. If people have the money to spend and don't mind, then ok. Just remember, it isn't used for soundproofing, it's used to absorb the energy that is being transferred through the wall and we don't want those sound waves to hit another barrier. That is why high density is bad.
3)it is my opinion that the layer of plywood or OSB some folks use can actually hurt the soundproofing of the wall. I believe it is the right thing to do in certain situations like where you mount a projector. I believe covering the entire first layer is a mistake. OSB is MUCH stiffer than drywall and as such will increase the presence of the coincident dip and raise the resonance frequency of the wall. The resonance frequency is the high pass filter of the walls sound transmission loss. The Coincidence dip is like the low pass filter. Mass primarily controls sound transmission between those two points. If we increase the size and lower the value of the coincidence frequency and raise the resonance frequency (and increase its amplitude/size) we have effectively reduced the range for which our soundproofing is effective. Use it where you need it, but don't use it just in case (unless you accept the impact on soundproofing).