I moved to US recently from India and I am looking for Plastic jars for storage,

It won't go unsafe if it's refrigerated or frozen, but it might pick up off flavors or turn rancid eventually. You can probably use it for 6 months if it's well-sealed and not exposed to air.

(1) Yes, that's fine. If you use freezer bags, you don't need foil even. For longer-term frozen storage, vacuum sealed bags work better.

(2) Frozen food stored at 0°F (or lower) is basically safe to eat forever. Eventually, the flavor will be affected and you won't want to eat it (but it won't make you sick). Three to four months is reasonable in tightly-sealed freezer bags. Longer in vacuum sealed bags. The storage time is entirely a flavor thing, so you can get away with a little longer for strongly-seasoned meat (e.g., tacos) vs. lightly seasoned (hamburger). The sell-by date assumes storage at around 30°F (normal for refrigerated meat)

(3) I believe so, stuff should still be good a few days after the sell by date.