To answer your first question I would be very worried about the long term health effects of ingesting chemically grown or unknown/street weed. I do not think vaporizing it makes a difference if anything it brings out the bad flavors even more so I would suspect it possibly even delivers more of these toxins as it does the cannabinoids. But who knows.
I've got to say from what I have seen over the years MOST people are smoking or vaping weed that is either improperly dried/cured and/or contains powdery mildew, chemical pesticides, fertilizer residues, mold spores, excess chlorophyll, bug shit, and all sorts of other nasties. Things you can't see with the naked eye. Its very hard NOT to get powdery mildew growing in humid environments or near the coast, PM is ingrained in the fiber of the plant so even if its not noticeable in the final product you are still inhaling the spores. Most all street weed is going to have some by product by the time it gets to you. I'm sure many of you will say you get from dispensaries so your weed is perfectly clean. Wrong. Dispensaries buy from growers but they aren't magic fucking wizards, most of them are amateur growers or old farts stuck in their ways. Point is their product is no better than if you bought it from them directly, sure dispensaries inspect the weed so you know it doesn't have bugs or visible mold or anything, but they are businesses and need to stay in business too. Also the weed is sold as soon as its dried, you aren't getting cured weed from the clubs.
The answer is if you plan to continue using cannabis long term you simply will need to find a professional grower/dispensary you trust or learn to grow it yourself. Organic growing is the only way to go IMO, and growing in a controlled greenhouse is ideal, because the sun has UV rays that HPS bulbs don't, so most indoor grown herb is missing terpenes and certain cannabinoids, true story. Organic growing outdoors is very easy and anyone can do it, also very rewarding. Good luck trying to find a good source of herb, remember its not just you fighting this struggle, we have whole the whole federal government waging war on safe access to organic clean natural medicine.