We keep stock of 5mg through 30mg vials, and most buyers go with the 10mg for initial dose-response work — it's basically teh sweet spot for early-stage trials.
Purity runs >99% by HPLC, and what that means for your assays is fewer side peaks messing with binding data; reconstitutes cleanly in sterile water or saline.

Storage is 2-8°C in sealed containers — don't freeze it, and we usually have stock, but confirm lead time if you need more than 50 units or so.
Microbial limits are <10 CFU/g, and our company can run sterility testing on request (usually 2-4 weeks turnaround).

One thing: this isn't suited for in vivo work without proper formulation help — the peptide degrades faster in plasma than some analogs, so plan your pharmacokinetics accordingly.
Also, we prep batches under cGMP with preparative HPLC and SEC, so you'll get a tighter tolerance than reagent grade for binding studies.