Please Help My Top 10 PvP Team

oTradeMark

Hello everyone,

I'm on a relatively new PvP ladder, I only started playing about 8 days ago and I've placed in the top 10 of the PvP ladder every day and I want to keep it that way but I'm afraid that with my current team I'm going to be pushed out of the top 10 soon because 2 of the characters I'm using right now are data card characters only (Grand Moff Tarkin & Dark Maul).

Here is my roster list:
http://imgur.com/7nXpjpP

I'm currently using Phasma as leader, Chewie, Grand Moff Tarkin, Jedi Consular & Darth Maul as my PvP squad.

Here are my questions:

1. How long do data card only characters stay relevant without promoting their star levels? Would a fully geared 4* Grand Moff Tarkin be any good against 5* or 6* characters?
2. I've heard that Leia & Qui-Gon are both really good PvP characters but when I tried them out they were terrible. Probably because I don't have their abilities or stars leveled up. If I was to level up their abilities would they make my PvP team stronger?
3. Based upon my roster list, what should be my short term and long term goals for re-adjusting my team? I've already invested a lot of credits/abilities/gear into my 5 PvP characters but if they are going to be worthless in the long run I need to start building up someone else to replace them. (Sidious, Daka & Lumi are the first 3 shipment characters I'm activating)