Answering this needs to know what is already in place, because the marginal value of each step depends on which are missing.
Handling risk is reduced by aseptic technique, minimising stopper entries, refrigerating after reconstitution and discarding on any change in appearance. None of it makes a preparation sterile.
Do not combine unknowns. Adding a second unverified compound while assessing the first makes any observation uninterpretable and doubles the exposure.
Independent testing of identity, purity and content is the only available check on research-grade material and is offered by several services this community uses.
Nothing here is medical advice, and research-use compounds are not approved for human use in any jurisdiction.
Test your own material. Everything else is downstream of knowing what it is.
edited 25 Nov 2024 by e_dziedzic — reworded for clarity after a comment