Yanfei build recommendations
Yanfei can have trouble trying to set up for her reaction DPS. Vaporize is generally the more consistent option and you need Xingqiu to make this work best. When running a Vaporize team with Xingqiu, 3 normal attacks into a charged attack (N1>N2>N3>C) is the safest and most reliable way to vaporize your charged attacks. Make sure you're applying hydro first before starting combos.
Regarding Weapon Choices
Bennett buff/ Thrilling Tales of Dragon Slayer's buff + Noblesse Oblige (4) will push Lost Prayer ahead of Skyward Atlas and Memory of Dust
Do note that with Bennett's Buff / Thrilling Tales of Dragon Slayer's buff + Noblesse Oblige (4), Kagura's Verity will push ahead of Skyward Atlas and Memory of Dust.
Note that with strong attack buffs like Bennett's Burst, an [R5] Widsith can outperform most [R1] 5-star weapons, with the exception of Lost Prayer to the Sacred Winds.
On equal refinements, Widsith is better than Dodoco Tales, but assuming it's [R5] Dodoco Tales vs [R1]-[R3] Widsith, [R5] Dodoco Tales is better. Note that Bennett buff / Thrilling Tales of Dragon Slayer's buff + Noblesse Oblige (4) buff may push Widsith and Solar Pearl above Dodoco Tales, even at low refinements.
Regarding Artifact Sets
Yanfei will rarely have her burst up due to the 15 energy cost on the 4-piece effect, however she can instead maintain the 4-piece DMG buff over a longer duration, making this set a good alternative to the other options. Note that this set loses out on some value at higher constellations, as she can't get her [C4] effects without casting Burst.
Actually her BIS if used in a full Elemental Mastery build with a overload team.
Running Yanfei with a shield character also allows you to make use of a full Retracing Bolide (4) as a placeholder until you're able to find a good Crimson Witch of Flames (4).
Regarding Artifact Substats Priority
Energy Recharge is prioritized over Elemental Mastery here since she has an 80 energy burst cost while her skill is also not very efficient at generating particles for getting it back. A major source of your energy will be coming from enemies as well as potential pyro batteries like Bennett, so be sure to have her pick the particles up as off-field characters only get 0.6x the value of the particles.
Artifact stats priority
crit rate, crit dmg atk% er em atk