The star metal that gets sold on day 1 does not have its clock reset. It will break even in 38 workdays whether you sell more star metal afterwards or not, any workdays over 38 on the early star metals help balance out shortfalls that come with not vendoring your later star metals. In my experience, the current amount of star metal can break even before the end of the demon general timer if you plan to mine them early, leaving you with a profit for the untimed content like the behemoth or Mount Firestorm. Level 10 Trademond workshop is still worth pursuing for the ally exp and will probably become more practical as new content gets released.
Half of those 76 days can be used to buy/learn upgrades/skills, and it nets you 114 max hp in the process. Depending on how much health you manage to burn at the festival, that's up to eight blessed waters worth of invest:purification that you've managed to crawl back from, effectively giving you an extra 16 days before soul break, or two extra uses of star knightess.
Verdeaux workshop level 1 also unlocks a 1200 gold +2 def and a 1600 gold +2 mdef, which is competitive with buying a scorpio claw from the restocking vendor. Decent for one of the late star metals, like the one behind the hydra(assuming you didn't new game+ the bubble to star knightess that one). The artifact it unlocks... maybe on runs where you don't have to buy church skills.
I don't use rampage or tenacity II much these days. Too much multi-hit bullshit at the later stages and too high enemy defenses on nightmare means a glass cannon Aura + slime tank build feels less reliable than opting for a +2 attack or +2 defense to stat check your enemies instead. Which is part of the reason why I recommend burning a lot of max hp during the festival after you unlock starshine.
The farmer thing is mentioned on the wiki and its linked pink run walkthrough. It's not really a secret. Doesn't give a lot per day, but it can reduce the number of times you work at the brothel.
Bloodshot eyes can be a decent substitute for radiance I or star knightess during the Belphegor fight but again:
Disregard cacophony,
Demolish collar.