Alright, bwos. I went and ran the numbers.
To get a character from 0-90 you'd need 1,876,600 shell credits. You would additionally need 1,750,000 shell credits to max out all their skills. Additionally, you would need 1,470,000 shell credits to take a weapon from 0-90. If we sum these up and additionally multiply by 2 we can ascertain the budget for rolling both Cartethyia and Lupa + their weapons and maxing them all out: 10,193,200 shell credits.
Furthermore, we can elaborate upon these by material requirements for the resonators(as the weapon ascension materials remain unknown). Characters need 46 of a boss drop and 60 of an overworld collectable for full ascension. At max sol phase, bosses drop 4-5 of their ascension material. On average, you'd need about 10 or 11 collections to reach this. However, since both characters use the same boss drop we can about double that to 20-21 average collections. Assuming you go into the patch with 240 waveplates and 480 stored waveplates that would be enough to immediately get enough for Cartethyia even if you roll 4 and never 5. In addition, 26 weekly boss drops are required for skill maxing. These are for old bosses are can be pre-farmed.
In terms of the other common enemy drops and forgery materials, Cartethyia requires tidal residuum & metallic drip while Lupa requires howler cores and waveworn residue. You need 32 of the green, 40 of the blue, 49 of the purple, and 52 of the gold for the enemy drops while needing 28 of the green, 28 of the blue, 44 of the purple, and 56 of the gold for the forgery materials in total to max out the skill tree.
So, to max out Cartethyia and Lupa you need:
>10,193,200 shell credits
>92 boss drops from the new boss(1200 or so in waveplates)
>60 of each new overworld collectable
>26 of Hecate's drop
>26 of Fleur's drop
>32 green tidal residuum
>40 blue tidal residuum
>49 purple tidal residuum
>52 gold tidal residuum
>32 green howler cores
>40 blue howler cores
>49 purple howler cores
>52 gold howler cores
>28 green metallic drip
>28 blue metallic drip
>44 purple metallic drip
>56 gold metallic drip
>28 green waveworn residue
>28 blue waveworn residue
>44 purple waveworn residue
>56 gold waveworn residue
Not counting weapons.