I sailed Seaside YC Interior with a friend but will be sailing with DH on Meraviglia YC Interior this summer which I hear might be a wee bit smaller than the inside on Seaside. Storage is limited so we packed a lot of removable hooks for hanging swim suits, coverups and such, it was fine and we were2 women, lol. I booked Deck 16 both times so we are on the same level as the lounge. Dinner is anytime you want to go I believe from 5 or 5:30. I thought food in YC was good. YC and Aurea are different areas. YC has it's own pool, hot tubs, buffet breakfast and lunch but the dining room is also open for breakfast and lunch as well. Aurea guests not allowed in YC area. We did have access to spa but never checked it out. Can't comment on uni-sex toliet but on both Seaside and Seashore there was separate public restroom on 16, one for men, one for woman. We usually tip above the basic grats.
Hope this helps.