I have Schultz Instant insect spray. A. Ivy is hard to grow here. Dexol Systemic Houseplant granules should control the scale. I would propagate only a clean part of the plant. Isolate the ivy from your other houseplants.
Spider mites can also attack ivy.
If they appear, take your plant outside in a shady location such as a screen porch and hose it down with a strong jet of water to wash away the mites. My pothos has some yellow leaves but most of the plant continues to look good. The leaves from my spider plant fall off every six months or so. The answer to all four questions is the same . No leaves are permanent and the lower leaves of all plants will drop off as new ones grow.