So you've defeated the Golems. You must be pretty proud of yourself. But the real threat is the enslaved Tiggy and his minions. That doesn't mean you don't have any time to explore the village. You might find something useful.
The first building to explore is the barracks. Inside on the first floor you'll find some armor and weapons of the Flowey Guard. You shouldn't take those, the guards may need them. But that doesn't stop you from taking a sword from a chest on the second floor!
Next it's time to hit up the shop. There are two sellers there, a husband and wife duo -- how cute. To the left you'll find a woman selling weapons and armor. Make sure you buy all the best equipment for everyone. On the other end of the store, to the right, is a man selling potions. As you'll find out soon, you will need a LOT of these for the next section. I recommend:
You may have to do some grinding in the mountains to make enough gold to buy all of those.
Immediately North of the shop, is the local pub. Might as well check it out. Talk to the bartender. He'll give you his most prized possession: a bottle of juice. You only get one so use it wisely (see other chapters!) Don't worry, it's non-alcoholic. The two men drinking at the bar are friendly but don't stick around there. The lady in the corner seems to be missing a key! Well remember that, because you'll need to find it for her.
Next building on the list is the fancy bricked library. On the first floor you are greeted by the librarians daughter. That's her job. Downstairs you'll find the librarian. Rios is of course very interested now, and makes a deal with the librarian to rewrite Seaside's history -- after battling the enemies on the beach.
In the tall grey building at the north of the village, are a bunch of monks mediating in the sun. Talk to them. They'll give you some good tips.
The last building, the one with the "Inn" sign on it, is the Inn (seriously!) The innkeeper tells you there is a room on the second floor where you can sleep. Take him up on that offer whenever you need to refresh and you're in the area. On the second floor, besides the empty room, you'll find some people who fled their home when the monsters came. The man in the Northwest room, amazingly enough, found the ladies key and is willing to trade it for the ring you've been carrying (you got the ring right?) Remember to head back to the pub and give the lady her key! Other people on this floor are a farmer and his wife who invite you to their place when the danger dies down a bit, and another lady who is anxious to get home.
More people from the surrounding area are taking refuge on the third floor. Talk to them if you're interested.
Go back to the pub to give the lady her key. She'll even give you a fancy gold medallion (that looks like it has some strange powers) for your troubles.