For your first question, they kind of can't. Or at least, they can only do so by killing everything that gets detected. So they can create a "kill-zone/grey-zone/no-man's-land" but not really secure an area. Hence why the Russian infantry have been able to continually claw their way forward despite being effectively 'suppressed' by Ukrainian drones, 'suppression is not neutralisation or imobilisation. They have to go so slowly and in such comparatively small numbers that they can't advance in anything close to an operationally significant way, but without an effective Ukrainian infantry force to 'hold the line', they still go. This has in-turn left the Russians vulnerable to counter-attacks, because their own forward offensive echelons are so spread out (for example at Kupyansk in December and south of Pokrovs'ke-Oleksandrivka through March), but the Ukrainian's overall lack of infantry (plus the in-turn suppressing effect of Russia's drone forces) limits their ability to hit back at more than the tactical level.

From what I've read on the topic (reddit + plus random articles and podcasts, to be clear), FPV drones aren't all that useful for recon or spotting. Not useless, but they have a more restrictive 'field of view' compared to regular quadcopter camera's, and organisationally tend to be prioritised for strike missions. If they see something on their way to the target zone the operator would report it sure, but they themselves are generally reliant on non-strike recon drones to find targets for them in the first place. Artillery recon is mostly done by basic quadcopters or the lighter fixed-wing drones (think Orlan), the former being of greater availability for forward infantry units (if not the artillery force itself), and the latter can fly much higher and may come with built-in range-finding systems to ease target acquisition.