eating the first product of the season make one live longer / a wonder lasts but nine days

(Shinto) the gods of calamity or misfortune

radish, Raphanus sativus, (specifically) small red radishes

(literally) know the other side and yourself, a hundred battles will not be perilous

exhaust / use up / run out of / deplete / befriend / serve

Kyūjitai form of 尽力: exertion

“a hundred days of sermonizing, one fart” → a metaphor for how something that one has put great effort into can come to nothing after even a slight mistake, much as a hundred days of serious spiritual study can be lost to the winds

plan, strategy / to omit / to abbreviate / to invade

(literally) plan your day during the morning, plan your year during New Year's / early planning is the key to success