Clearing Storm Difficulty.

Storm enemies have a bit more hp compared to Thunder node but I think that's about it. It should be possible if one used servants with class advantage. I've been running Mountain on Storm difficulty using Saberlot(lvl 60), Ridertoki(lvl 80) and Cu Alter support and a bunch of lvl 1 bonus servants on back line. It would be a lot easier if I could use assassins but Heroine X is the only good assassin with the correct bonus and I don't have her on my support and I only started FGO during Onigashima.

Storm is 2x more difficult than thunder. Leveling your servants (atleast lvl 60) and their skills will do the trick. Also make use the class advantage.

Depends.i'd say a lvl ~65 and above SR and a max R with Mash/friend support would do the trick