1. Each one tracks it's nearest neighbors, which should have approximately zero differential velocity. A few gyroscopes or actuators to change the mirrors angl

1. Each one tracks it's nearest neighbors, which should have approximately zero differential velocity. A few gyroscopes or actuators to change the mirrors angles should give you plenty of thrust for controlling orbits. Inevitably probes will drift outward without counter thrust, after all they are basically solar sails. You could also use lasers, microwaves, or similar to cooperatively fly together without colliding. Of course you don't have to be perfect, just good enough that more expensive solutions aren't worth it. 2. Why bother? Make fuel, like antimatter for instance. Then launch them to where you need them. Maybe by a relay system and you could use the kinetic energy to help keep your ideal orbit. Keep in mind these don't have to last forever. Maybe have 3 different designs for how close you are to the sun. Then you get installed in the inner most orbit of that band, then during your useful life you edge towards the outside edge of the band, launching anti matter payloads periodically and then get recycled at the outer edge. As long as you collect significantly more energy than your production cost it's a big win.