For the second, Γάμος is like the word "marriage", meaning both the occasion of getting married and the state of being married. So a better translation would be "Master (your) marriage". Given the Ancient Greeks' dim view of women, I'm guessing it boils down to "Wear the pants at home."
For the third, I think it should be "Cause no grief onto [others]" (ἐπί+ dat.)
My guess is that rather than "always be thrifty", this is more like "don't let cost-optimizations stop forward progress". So, somewhat more like "penny-wise, pound-foolish" or "don't let the perfect be the enemy of the good" than "always be thrifty".
Master wedding-feasts
My guess here would be a meaning like "take full advantage of important ceremonial celebration feasts", with possible connotations of both "enjoy them fully" but also "don't over-imbibe or take them for granted".
Grieve for no one
Could very well be dependent on the exact form of 'grieve' in the original formulation; if a word meaning to mope or remain backward-looking (as opposed to honoring/learning in memories), it might really be about doing the right kind of mourning. Or, if the emphasis was on 'one' unique person, it might mean never to focus grief on any singular loss, as loss is universal – sort of related for "ask not for whom the bell tolls – it tolls for thee".
I think this might be a mistranslation. Maxim #118 has the same last two words in Greek, and is translated as "Do not abandon honor". So #122 is probably better translated as "Do not abandon thrift", or "Do not forget to be thrifty", or something like that.
https://en.wikipedia.org/wiki/Delphic_maxims#147_Delphic_max...
The last is, fittingly, the most meaningful of them all: On reaching the end be without sorrow.