It sounds as if it need a decent service. Sticking stop down lever is a sign of the lubricant drying up and the sticking shutter is almost certainly sticking electromagnets. All curable with a service. These things don't go on forever without a bit of loving care.

Likewise with the lens focussing, it is just the lubricant has dried up. When you think that an R4 + lenses are almost certainly 30yrs old it is overdue.