Will one session be enough?
Almost never. Sun spots clear in 2 to 4 sessions; melasma is its own question, answered below. After the first session I can say how many more it should take.
Picosecond light for pigment, scars, and renewal.

The same Candela PicoWay® as the tattoo work, with the Resolve handpiece fitted and tuned to melanin instead of ink. Short pulses break excess pigment into fragments the body clears over the following weeks; at other settings the same pulses work on acne scars and fine texture. Not the only tool I have for pigment, and not always the first one I reach for.
Treated spots may darken and form small scabs over the following days, then shed on their own. The skin around them stays pink for a day or two. Do not pick anything.
Almost never. Sun spots clear in 2 to 4 sessions; melasma is its own question, answered below. After the first session I can say how many more it should take.
Yes, with caution. It is chronic, and pushed too hard it worsens, so I start at the lowest setting and reassess after each session. Expect control, not clearance.
Yes, with SPF 50+ every morning and no skipped days. Practices in far sunnier places than this one run these lasers year-round, and with the sunscreen used properly, so do I. If a sunny holiday is coming and the sunscreen will not be reliable, leave two weeks clear either side of it. Sun on unprotected, freshly treated skin undoes the work, and can bring the pigment back darker than it started.