Keep in mind there rules are just a draft. They're a hodgepodge of D20 and D6 rules cobbled together, so there's a lot of cleanup to do.
Having said that...
How often could one last before needing their next fix?
If addicted, the penalty applies the moment the spice wears off.
I noticed you've got a price on Glitterstim at 6000-10000 a hit, I would guess that most people could only afford it a few times a year at that rate.
Glitterstim is very expensive. It is not a street drug, and you can't go to a typical supplier to get it. Addiction to Glitterstim can be ruinous in many ways.
And for breaking the addiction, the addict essentially has a -5 penalty for 4 weeks while they work to break the addiction?
No. It's -2 for two weeks, then -5 for two weeks. Then you're cured.