Why is this gallery named Watashi ga Yoso... instead of Tsuma ga Yoso...? I see the phonetic symbols わたし, but I'm not aware of that reading of the kanji 妻. Is it suggesting that the story gets told from the perspective of both the husband and wife?
Not both; I believe the meaning is close to 'I (who am a wife)'.
This is a fairly common (and rather fun) phenomenon in Japanese, showing the reader two sides of what the speaker is saying and thinking; for instance a demon king in a casual setting might say he wants to eat some food (furigana/yomigana, the 'read as' part) and the kanji (the 'written as' part) might show that the underlying meaning of the word spoken as 'food' is 'people'. Or in reverse, a disguised demon king in a social setting might say how glad he is to meet wonderful-looking people, but the kanji might show that when he says 'people' he means 'food'.