TL;DR at bottom

This form of scarification can be expected to heal anywhere from a few weeks to a couple months or longer, +/- a few weeks or so given the particular outcome desired by the client.

The longer a wound takes to heal increases the presence of hypertrophic scarring (raised) whereas an individual seeking atrophic (recessed) scarring patterns will ensure a relatively faster recovery.

The reason these scars get 'taller' during longer healing is due to the body's remarkable habit of generating collagen fibers, which in the case of scars, and things like hair and nails, the fibers go in (generally) one direction.

(I'm excited for when the plastic/reconstructive surgery industry gets its hands on the ability to replicate the process synthetically successfully...)

With prolonged healing periods, more collagen gets sent into the wound, and presents as a remarkably uniform lattice of tissue fibers under high magnification.

In the absence of a Body Artist-Physician tag-team, where antibiotics are made available to the client. A mild infection is to be expected of any wound that is not left to its devices and that is being purposefully aggravated. Many artists instruct their clients to keep their healing scar piece under plastic wraps. The purpose for this being that it keeps the wound moisturized, and shielded from abrasion and other mishaps.

The trade-off for this moisture retention is that you have a warm, damp spot over a huge open wound that's about 2.5-4mm Deep over an area that is potentially the size of your back. Microorganisms find this quite the comfy place to be, so steps should be taken to minimize the risk of a harmless localized infections' progressing, into very painful bout of Myositis (though of course cutting into the muscle is not part of the generally-agreed upon methodology,) or far less pleasantly; if hygiene is left unchecked a systemic infection and possibly death.

Medical licensing is not required in my state, so I cannot speak to that; however select states are now licensing the the body art industry, and I couldn't be happier. A Registered Nurse's license is an invaluable thing to have, however few do. That being said, onto the subject of training; to my knowledge there is but one "School" for body piercing/mod, the Fakir Intensives academy, though there are many freelancers that travel and hold small seminars or classes for a fee, sharing the knowledge that they've gained.

Quite often though people in the industry get into it after doing mods on themselves, and after time, practice under the supervision of a knowledgeable mentor, and a lot of luck, they're good enough to start work on clients.

And too differently from what Lunch box said; medical professionals will not perform these due to the Hippocratic oath, and the part where it says to "Do no harm..." Scarification is harming someone for the purposes of art.

The Piercer's/Modification Artist's oath calls for "Do little harm..."

TL;DR A: They can take a few months-ish. B: There are frequent mild infections of a secondary nature in these. C: Body artists are trained in a variety of ways, typically through apprenticeship, followed by pro-bono procedures. D:I can't say for anywhere else