99TurboFerio

Ive got a d16y8 that im running the greddy kit at about 10 psi kinda... its not very stable.... the greddy kit has an internal wastegate right? so how does that work exactally and is external really that much better. should i go for a new mani and get like a tial wastegate... i want to get a ball bearing tubo and get rid of the td04 ..i was thinking a gt28r? what will i need to put that in my car with the greddy kit already in? mani and wastegate? does it have to be a specific mani for the turbo to bolt on? i need help and explainations...