The game just goes through all conditions one by one, so you can unlock multiple cheats and outfits at once without problem. Not all of them though, since some endings require you to have certain skills higher than others. 999 food is the food resource you pay for working.
Relationship doesn't do much right now. Some NPCs will give you gifts if you raise it to like 20 and they will be considered your friend if you raise it above 50 (necesary for house upgrade and some endings). I will develop this part further once the game actualy has more things to do beyond year 1.