Thank you everyone! To answer questions:
1. I bought the pistachios already slivered, but I did shake them in a sieve to remove the dust
2. The flavor does seem stronger, but to me, it seemed more like a stronger nut flavor (like a roasted, nutty flavor) rather than an over-the-top pistachio flavor (although I think a lot of what we think of as “pistachio” flavor is actually almond extract). Don’t know if that makes sense. What I really like about them is the beautiful emerald color.
3. It is delicious and actually pretty easy to make, doesn’t take long. The pistachios were a fun splurge.
4. I think I pretty much followed what is written in the cake bible regarding applying nuts, although I haven’t read that part in a while. You need the cake on a cake board, and a sheet of paper on the counter, hold the cake at a slight angle close to the paper and toss the nuts up on the sides. They will grab onto the buttercream, which I chilled slightly to hold its shape, but not too much so that it will still be sticky.
I will also add that I used a combination of frangelico and amaretto in the buttercream instead of pistachio essence. I think it flavored the buttercream nicely.