Hi spiritual_thinker, and welcome!
No need to SWIM around the Nexus. It doesn't offer any protection, legally speaking. And sorry to say, but there is no talk about
sourcing materials anymore. Would you mind editing your post?
In regards to your question on DMT (I have no experience with Salvia unfortunately). My advice would be to have a sitter for your first time if that makes you feel comfortable, but it's not utterly necessary. It can be nice to talk about the experience with someone who knows you well to offer some insights or comfort though.
There are a few things to think about when delving into this world - state of mind (set, good mood, clam), your location (setting, safe and comfortable place, loose clothing, nice smells and music.. if that's your thing), the purity of the molecule (good extraction tek), your smoking device/technique (GVG or good bong for changa), and also intention can be key. If you have these things sorted, then a bad experience is less likely to arise.. difficult maybe, but this can be extremely beneficial. Specially when considering your reasons for going down this path.
I wish you well