- an NPC accountant contact the PCs have with Ares Arms with a drug habit has switched to tempo. I'm thinking he may eventually either sell the PCs arms dealing business out if it means he can score some more tempo (when things get desperate) or he may just be fired for his substance abuse problems (which affects their access to inside information within Ares).
- PCs have recently managed to get a large amount of BTL chips from stolen Lone Star evidence lockers (they were marked for destruction). They were planning on reselling them but unfortunately sales are taking a hit due to the popularity of tempo.
- PCs Vory contact (Unkle Nikki) contacts his 'favorite nephew' for dinner. Apart from discussing their burgeoning arms dealing business, Nikki expresses his disgust at how this new drug is affecting his business and predicts the escalating violence will only worsen. He will (politely) ask for a greater discount on arms from his nephew (they helped him to setup the business in the first place), in anticipation for the escalating conflict as well as 'ask' for him to restrict the distribution of arms to rival syndicates. He will also ask the PCs to keep him informed if they learn who is supplying the First Nations.
- A mysterious Johnson contact of my PCs (with connections to Tamanous and biomedical and some magical interests) wants to get a few samples of the drug to analyse the affects. He offers a job for the PCs to get a reasonably 'large' sample (say a dozen derms? not sure what would be considered large) as well as some 'live' addicts.

Regarding your first idea, I'd say that even with a substance as addictive as tempo, it takes some time until a user becomes desperate enough to start selling out trusted contacts and jeopardizing his business as a whole (of course, this may not hold true for someone who has questionable business ethics to begin with...).
I'm not saying that it's a bad idea, but i'd make sure that his habit develops to a point where effects become very visible and it's obvious that the NPC is neck-deep in trouble (probably as far into the habit as to become a viable target for spirit posession, but at least deep enough into it to have severe problems functioning normally in social situations without the drug).
He may actually be likely to get fired before he goes that far (which would also only happen if the drug's side effects start impeding the corp's bottom line, even though Ares may have a less lenient approach towards their employee's drug use than, say, Aztechnology).
Furthermore, it could be more interesting if the players start suspecting that their connection is selling them out, even if he's not yet actually decided to do so.
I'd make sure that the personal decline of NPCs in the campaign comes across as a visible, but gradual process and that the PCs start wondering how far they can trust a notoric tempo tweaker.

As far as the fourth idea is concerned, i agree with Jaid here.
Getting enough samples for analysis is no problem, you just walk up to one of the many upcoming tempo pushers in the sprawl and score some hits.
But, as Ghost Cartels shows, a chemical analysis won't get you very far with that substance- this is where a team of runners may come into play, tracking down supply lines to get as close to the actual source of tempo as possible.