Hi again
for your first question I don't have the exact numbers, but i know that finding floryns and potions is more common than finding accessories creatures or jewels
it IS worth it to send all your creatures, it gives you more chances to get something (and more chances to have a creature with a accident too ^^")
the country where you send your creature will only change the potion you can get, for exemple you can only find Night elixirs in Renarhim. For the rest, no, just know that if you send your creature in an other country than the one it lives in, it will take more time and energy to explore