Are you sure you want to use that whole 20K for upgrades? If so, you have lots of options. Since you are probably young, my personal advice would be to use 10K for car stuff and 10K for investments. Open a Roth IRA at Vanguard with 5K, and put the other 5K into a money market fund at Vanguard to get a good start on an emergency fund.
OK, I'll get off my personal finance high horse...
The FEED final drive is nice for low end acceleration, but if I had a 20K budget, I'd just skip that step and go straight to FI (forced induction).
But if you are new to car modding (like I am as well), you either need to find a good local shop or some trustworthy local enthusiasts to help you out. Especially with FI, there is a lot of stuff to consider. I haven't done FI yet, but fortunately I have found a few locals that have ended up becoming good friends as well as helping me out with mods to my car.
Considering you are new to car modding, I'd recommend one of the Mazsport turbo kits. They are pricey (8 to about 10K, depending on the kit you choose), but they come with everything you need, except perhaps gauges. They don't require you to do additions/modifications like the Greddy kit, etc. Plus Scott (Mazsport's owner) is known for incredible customer service.
What is your location? Post it here and we might be able to help hook you up with a shop or group near you. My advice would be to find a local RX club, or a good local shop.
As far as suspension mods go, sway bars seem to be the logical first step for everyone. Best bang for the buck. That is my next planned mod, probably Racing Beat sway bars. But any of them will probably help you improve the body roll if you like to corner aggresively. I don't think any suspension mods are needed, though, unless you plan to do some track days or autocross. The 8 has almost a perfect street suspension stock.
The best handling mod would be good summer tires. I choose to run ultra-high performance all seasons because our weather can be so erratic around here. I've had them to one track weekend and they did fine for a newb like me. I went with a bit wider tire than stock to help make up for some of the dry grip I lost by switching to an all-season tire compound.
If I was in your shoes, I'd be thinking about the cheapest Mazsport kit, which you can see here: http://www.mazsport.net/store/index....ct_detail&p=12
But before you do that, do lots of reading here, books, etc. If you don't have local buddies to help you do the install, you will have to pay a shop to do it for you. By the time you pay a shop to do this turbo kit and some gauges, you will have gotten close to the 10K. Then you can slowly mod your car from there.
I've found it is fun to do one mod at a time anyway, rather than do a bunch at once. That way it feels like you are getting a new toy every so often, rather than just one big new toy
Another thing to consider with your location is if you have to deal with emissions inspections. There are ways to deal with that with any FI kit, but you'd have to be comfortable disconnecting it, or be ok with paying a shop to disconnect it for you. Depending on the kit, it is usually not a big deal to disconnect. But if they do a sniffer test and not just an OBD port scan, you might still run into issues.
Like someone else said, please post what year AT you have so we can help you out more.
Sorry for the long-winded post, but I was in your boat not that long ago. And since I'm a veteran, figure we gotta stick together
Thanks for your service, and stay safe!