I agree with everyone else, grab the Beginner Box and run through it with your group. Really, to get started, that is ALL you need. You don't even need to read it before you start playing. Just sit down with your group and turn to page 1 of the Adventure Book.
If you're not using maps, minis or tokens, a good way to keep track of it is to continually describe the ranges in your narration.
"You turn the corner and you're confronted by a group of 5 Stormtroopers at Long Range. One of them points at you and shouts 'Halt!'".
"Two of the Stormtroopers move forward to Medium Range and take cover behind some crates. The remaining 3 at Long Range duck down behind the corner of a wall and fire at you."
"Okay, Lowhrick, you've moved forward to Engaged Range with the group of 2 Stormtroopers, you're now at Short Range from the group of 3. The rest of you are still in cover at Medium from the group of 2 and Long Range from the group of 3."
...and so on.
It gives you a lot of flexibility to say "There's a shop window here you can dive through to take cover", or "there's a speeder bike parked in an alley that gets shot and explodes". Lots of times the best stuff in this system happens on the spot, without having been planned.
On Overpowered Characters:
I guess it's possible but it takes a real min-maxer's mindset to do it.
As a GM, it's pretty easy to adjust encounter difficulty on the fly, to provide the right kind of challenge for your party.
Is your nemesis getting shot more than you expected? It's easy to add a few more points to their Wound Threshold, or adjust the damage their weapon does, or to create new environmental effects to make it harder or easier on your group.
Often with my group I find that I barely need to write down stats for a character. I just need a general idea of their wound threshold, soak, and damage they do. I tend not to create super-detailed Nemeses for the characters, in order to keep the game flowing smoothly.