Don´t forget death, you have no old mages so a little bit of death is a good choice, remember that you can build castles underwater, and recruit a nice good mage, but he is coldblooded.
My recomendation is an awake rainbow, i usually choose the crone/enchantres and focus on manual site searching, THE KEY to JOMON is gems a lot of gems.
Scales: order is a must, also a little bit of production helps a lot with expanding, but 1 or 2 no more. Heat is good for points and it works with your underwater mage. Death is a very good choice for Jomon, no oldage, i usually take 1-2 death. Magic/drain depends on luck scales, i usually go for magic 1 and neutral luck/misfortune. You can tweak these sacrificing magic paths and get order 1/prod 3/heat 2/death 2/ luck 3 and magic 1 or drain 2.
For the magic paths: remember that you have natural acces to all but death and blood paths so you can remote sitesearch easy and free your pretender from manual site searching once you get good death income. Focus your pretender:
-A4 for boosters.
-D4 manual site searching and national summons, Dai oni is good BUT Ghost generals AKA Shura are really cheap good thugs undead/fear/ethereal for 6D gems.
-F1 Skull of fire and Dai oni and if you feel generous F3 for flaming helmet.
-S 3-4 rings
-N 3-4 Mother oak/regeneration to your holy spirits AKA Kenzoku. Or nature 0.
-E 1+ dai tengu
-W 1+ well you are manual site searching anyway.
Holy **** i should write a guide
. Remember your national summons(conjuration school) the Oni general requires 2d to summon and he comes 1D +1F/E/D100%.