There's no "magic bullet" to getting good recorded/mixed sound... It is a combination of different things...
When I first got into recording about 8 or so years ago, I purchased the Digi001 and soon thereafter a Waves suite of plugins... The Digi001 had 2 mic preamps and 6 analog in's...etc, more than at the time I though I'd ever need...and with the Waves plugs, I 'knew' I'd never need anything else... Well, here some 8 years later, I've got a bunch more stuff... You soon "grow out of" your low-end mic preamps, compressors, EQ's and AD/DA converters...
With you just starting out in recording, yes, you probably have "everything" you need to get started. When you arrive at the point to where your skills are good, but your equipment is the biggest thing hampering your recorded sound, you'll know it...and by then you'll have done many hours of research, many hours of recording and mixing, and will have a very good idea of what "more" equipment to buy and most importantly, WHY.
I hope you don't take my response as being mean or sarcastic, because I had the very same questions when I first started...and it took me a while to figure out why no one would/could answer me... really there is no correct answer...
Sonic Maximizers: Well, I wouldn't go there... I've tried them as has most everyone on this board, and they just mostly hype the top and bottom ends...nothing you can't do with any EQ.
That rane unit was fantabulous!