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i would suggest getting an external sound card/IO interface. it will far exceed the capability of your computer's native sound card, making the idea of adding many tracks a lot less worrisome. it will also give you the added advantage of having ports nearby that your can plug stuff into, and a volume knob that you can physically shut a haywire situation down to zero volume with. that sh*t can freak a motherf*cker out!

reason is an incredibly powerful program. it doesn't work like other programs in a lot of ways, so it can be kinda weird to get into. one reason it's being used so much though, is the combinator. the combinator allows your to take pretty much as many different virtual instruments/samplers/effects as your computer can handle and turn them all in to a single instrument, layered and routed to whatever effect you want. this has the ability to make insanely huge sounds. you gotta know your sh*t though, cuz it might sound good coming out of your speakers at home, but if you don't know how frequencies work, take that track to a club and it might destroy their sound system... or just sound terrible, which is embarrassing.

i would get reason for the sole fact that you can open it as a plugin inside...

FL Studio. i've been using FL Studio since its inception. the creators of it wanted to make a program that anyone could make music with, no matter what level of ability they had attained. by all counts, i would say they've quite succeeded in that endeavour. i've used a lot of different programs, and i always come back to fl studio. i also find it to be the easiest on the eyes, on top of being extremely intuitive. and like Zebras said, you can find a lot of tutorials online. you can also find a lot of tutorials on Reason though. they're just weirder.

the one main thing i really want to suggest though, is DON'T BUY A MAC. unless you have a sh*t-tonne of expendable cash. with a pc you can find ripped versions of pretty much anything you're after, try it out first, and then if you end up using it a lot you can buy the real release, which comes with some perks like automatic updates and tech support.

EDIT: i said getting reason to open in fl studio was a good idea because using reason alone to record and sample and arrange is a pain in the arse, but if you just want to use the instruments and effects in it, that can be done without having to bother with reason as a sequencer. just clearing that up.

EDIT #2: having two or three monitors will greatly increase the fluidity of your workflow. making music in a DAW can get pretty hectic with all the little windows you might have to open up, so being able to spread them over several monitors is a huge plus. i would pretty much call it a bare necessity.