Store pickle, spices, dry fruits? I'm not sure if that's a food-grade jar. I would recommend pickling raw (ripe is used for sambar) Malabar cucumber. But then again, you won't be able to probably find it in your stores. Or better, buy black pepper in bulk, throw them in a mixer grider, turn it to power, and then store it.
Yes, it is, but glass can be contaminated by previously carcinogenic and not-fit-for-consumption substances. Simply scrubbing with soap and water isn't enough.
Huh? What jar bought from a store these days is going to have that issue? There is uranium glass but even the cheapest cheap shit glass from the dollar store is going to be safe for food storage. Glass isn't likely to leach out harmful chemicals like plastic can. Plus glass doesn't absorb anything that could then later be harmful, that's why glass is used for canning among other things.
Old glass can be quite dangerous - carnival glass is especially notorious for contaminants. Glass is tricky and a lot of cheap glass intended for display and manufactured abroad may still not be food safe.