IMO, it sounds like you're on the right track. #1 instrument(s), #2 workstation, #3 Monitors, #4 DAW...
As for the software, a lot of it boils down to your experience(what you learned on) and given the kit you've already got, you might not want to rule out building a Pro Tools rig(I think that's the first and last time you'll hear me say that.) Here's why tho; I'm assuming you're a rocker since you play the drums and guitar. Pro Tools is argueably the best for audio editing and while it lacks a bit on the MIDI sequencing end, it doesn't sound like a big concern.
That said, Cubase, Sonar, Reaper, Logic are all fully functioning DAWs and can get you nearly any place you want to go. None of them are particularly more useful or compatible with the Fantom-G than another. Ableton Live fits in here too, but has a particular bend for 'live' performance and looped material. Fruity Loops is noteably another good place to start, but more often used for dance music.
Inevitably, you're next step is going to be choosing an interface; another reason I threw Pro Tools in there. One of the first things you should consider, beyond firewire/usb is how many inputs/channels you're going to want to record. If it hasn't already, switching plugs and adjusting levels in and out of the Fantom is likely to become a chore.
Keeping that in mind, you can start adding up the dollar signs. You might want to save a few for cables too
and if you're serious about recording other people and producing, that's another huge can of worms(read:dolladollabills) to spend on your room.
yeah i wish i could afford one. 
. The sad part of my story is that I just upgraded from an old receiver and regular speakers, to a some mackie Mr8 monitors (which btw I am very satisfied with!). Also, I'm not too constrained by spending money. On the other hand, I don't wanna wind up like "the extreme", with a "music shop" worth of equipment because i didnt buy the right stuff in the first place. This is obvious i Know...sorry. Ive always been under the impression that mac's are what professionals in studios generally use. though on the other hand, a computer is just the parts put into it, and yes Artemiy, Macintosh has a extremely good reputations for the their computers and customer service (though I'm not sure the same can be said for the I phone-not that i know personally). Bottom line is, right now i have a hp slimline pc, and I'm leaning towards picking up a lite version of cubase. All I'm working on in the near future is recording mostly myself, but some friends as well. (I'm a drummer with a sweet roland v drums kit! But I also play guitar and obviously keyboard! One more question (for now). Artemiy, I'm interested in these mac mini laptops or maybe even a full scale laptop. Not just for this audio recording but they seem pretty cool in general. Anyways, what is it that makes them preferable for recording over a pc? sound cards? processing power? Can someone please explain. btw Art, I didn't feel as though you were trying to "sell" me. why is it people are accusing this, do you work for mac or something? Once again thanks for the help everyone.
