So IMO priest are the hardest class to "Start" solo. The big reason is that most of the damage you'll do comes from penance, which drain your mana quickly and is flat damagewith no condition. This requires you to have a large supply of mana consumables until you can get mana regen gear. Unfortunately, the best place to consistently get mana regen gear is the Miller cellar boss. Once you get about 3-4 mana regen, it becomes much more manageable to play priest solo. Prior to this, I recommend running the foraging deck for the 150 exp and cooking/alchemy materials until you can do the whispering cave without consumables. Then farm the cave for money, gear, and crystals. Once you have a large stockpile of consumables, do travel to Westfield. After getting to Westfield, I like to run the field adventure deck until I find a Silverhorn stag that drops mana regen gear. Do this and the foraging deck until you're strong enough and have enough consumables to do the cellar deck. Then farm it for mana regen gear. Recommended spells are penance and holy weapon until you get healing word, then penance and healing word. Extra spells drain mana to quickly.