Heartstone info

What are good maps to farm Heartstones at? I've been going through the Mushroom Kingdom maps lately.
How often do Primal Essences drop?
What's the respawn time of a Heartstone (if there is a set one)?

In unpopulated maps. Mushroom Kingdom is a weird exception probably because you get a profession at level 30 and the quest that introduces you to Mushroom Kingdom also automatically teleports you there, not giving you a chance to get your profession until you leave.

Well, I can't really answer your question for how often Primal Essences drop, but I've found that the Sky Terrace maps in Ludibrium are a great place to farm just about all of the different veins, as well as heart stones. Just run from one end to the other, CC, and repeat. You could also try the Robo maps just under the Sky Terrace, as those ones loop around, allowing you to go from one end to the other and then down a level, then travel back to the start and finally CCing to repeat.

Qualities of a good heartstone/gold flower farming map
Has multiple different spawning ores giving the heartstone more of a chance
Quick/easy to maneuver so you cycle thru all chs faster
Unpopulated so you are the one who gets there first

I prefer the random maps in kerning mall outside the main ones, hardly visited, flat,and spawn a lot of ores. Heartstones spawn every 24hrs but I believe you would have to go to the map daily (outsides sc's) and mine for a rare chance of one spawning, for these cases I like to mine purple veins while I mine, good maps for that is orbis tower.

Rarity of primal essence, I've never got one, never seen one in my world, and the one primal essence that was duped from scania to make the dom pendant ectect was bought for 20b I hear,, to give you a sense of the rarity

I used to run through Dead Mine 1-4 when I farmed Gold Ore for Gold Hearts (when they were actually worth something and no one had recipes) and ran into Heartstones pretty frequently.
You could try there.