50 jewels per day from dailies
240 jewels every 12 days from the standard login bonus
(long term average of 20 jewels per day from login bonus + 50 from dailies = 70 per day as the expected baseline just from being active)

Advent events = 200 (50 jewels for each of beginner/standard/expert/ultimate) + up to 3000 (exchanging for 30 jewels at a time)
Raid events = 300 or 350 (50 jewels for each of standard/expert/ragnarok, 50 jewels for each story segment) + up to 3000 (at 225 blue souls/95 red souls) + X (how ever many sets of 5 jewels you roll from raid gacha)
Union events = 400 jewels (at 500k union PP, 14 expert kills, and 26 ult kills) + up to 1000 (from expert kills rank) + up to 1000 (from ult kills rank) + up to 3000 (from individual PP rank). The realistic floor is probably 400 (the guaranteed rewards) + 300 (expert rank 31-350) + 750 (ult rank 16 to 1000) + 1000 (individual rank 501-1000) = 2450 jewels.

Then there's random stuff like special login bonuses for whatever reason or collabs/promotions that's harder to predict. Although I'd say that recently one can rely on at least 1000 jewels a month from random special login bonus.
If you want to be conservative with your planning, you can lowball your jewel income at 'one 10x roll per event'.