Jebus,
After 10yrs of flightsims and probably 100's dollars worth of professional addons it can get to be very expensive once you start getting into purchasing pro addons. For FSX imho there is only two professional companies out there that make planes worth the $$
And thats, PMDG and Level-D... Others like Wilco Publishing are good but just not cutting edge like the previous two. Captain Sim are good but only their C-130. Flight1 have some fantastic props and the excellent ATR 72-500. Stay well clear of any software classed as "light" it's expensive and a waste of money.
The most fun you can get out of FSX imho is flying on Vatsim (which is free!). When you take it online is a whole new experience and far more rewarding then flying offline.
To really get involved and start a virtual pilot career so to speak. Start off with the basic twin props and fly online, start off with small airports and work your way up. Once your comfortable with ATC/procedures move to a Turbo Prop like the Flight1 ATR 72-500 to begin getting use to working with FMC. By now your'll have clocked a few hours online and know ATC,Airport SID STARs procedures pretty well.
Then start looking for a Virtual Airline to join and learn more from them with fly ins etc but also sharing vast amounts of knowledge. VA is like joining a squad research and ask questions search the AVSIM forums for feedback on different VA's try join one that's very well established. And preferebly based on a real world airline. If you have a few hours on vatsim and show that you've made a gradual learning curve rather then jumping into a 744 and unable to read an approach plate you will be highly sort after.
Then start getting into the heavies, by now you'll know whether you like short range 737s,A320s etc. Medium 767s or Medium/Long 744s once you start getting into flying 744s in and out of busy airports you'll thank all the time you spent hours with the ATR 72
Before you know it you'll be able to join the likes of Polar Air Cargo and flying 742s all over North America and Europe.

As for professional addons other then planes I'd stay clear of all of it for FSX. My order of importance/pref for addons and FSX would be as follow:
Flight1 ATR 72-500
Level D 767-300
PMDG 747-400
FSG Global Mesh
Global LandClass
That's it. If you like flying Australia then without doubt Full Terrain Experience is incredible and the best scenery addon combining mesh/landclass and textures ever released.
You can easily spend $1000s of dollars on addons, take your time and only purchase the very best.
<S>...-Gixer