To get Tina, go to the Beegees Town, and go into the church. There talk to the man in the black and you'll end up fighting badman's. After you kill all of them talk to the girl on the floor, and she'll join you!
To get the Dog Pill, go to Beegees Town, and walk out the North End. Go to the cave, and walk through it until you reach the Badbad's house. Go through this house until you find him himself. Rest in the bed before you fight him. He will tell you, you went through the wrong door after you defeat him. Once you do defeat him go through the door, and there are 8 treasure chests waiting for you, one of them has the dog pill in it.
To get to Decatas, first go to the Giant, from there go around the trees and approach a hole, and talk to the man, while speaking to him if you pay him 100 gold, he'll happily dig you a tunnel to Decatas.
There are several Kustera Members who cannot be found normally through the main story, Ben is one of them.
To unlock him you must talk to the woman in the rightmost house in the group of three in Decatas. Then go find Ben in the nearby bar in the main district.
There are several Kustera Members who cannot be found normally through the main story, Evelyn is one of them.
You can find her in her house in the near entrance of the Elekees.
There are several Kustera Members who cannot be found normally through the main story, Ryu is one of them.
Right after you have defeated Badbad use the dogpill, he is in a house in Beegees. Talk to him and then he will join you.
There are several Kustera Members who cannot be found normally through the main story, Shark is one of them.
To find Shark in the house southwest of Bonzley you will need to have gotten Dan. So right after getting Dan head to the house in Bonzley.
To get the Graviton that allows you the ability to shrink Golan, go to Decatas, and walk into the lab. From there, go upstairs and talk to the man standing there, let him join your town and next thing you know you've acquired the Graviton!
When you reach Decatas swap for Kustera and go to Decatas without killing anything. Then, enter the government office and talk to the woman she asks if you want her to bribe the guards. If you have not earned any money with Kustera (besides the money that they start out with) answer "Yes" and she will bribe the guards. Your gold will turn into the maximum amount for Kustera.