I am not to fond of the sound of an under powered integrated circuit, so when I use gear that has them stacked end to end I try to bring stuff in as clean as possible to avoid emphasizing that sound character.
There are so many ways to get stuff done and do it well...
If you are really curious about a hardware compressor and you are going to get to learn about it then it seems like buying a compressor that you'll enjoy for years would be a good start. If you find that using the insert patch on your desk sounds good to you then you will not have to re-patch all the time. If you try it the other way and enjoy the sound better then that's good too. Either way, you'll end up with something nice.
If you buy a 4 banger compressor it's going to sound like utility compression and color your sound with goo. Maybe you will hear it, or maybe you will not.
There is no way to build a compressor out of less parts than a pre amp. Think about what you like about your pre amps and then figure that a compressor of similar quality will cost a bit more than the pre amps you like.
One of the most influential parts of a free standing pre amp (or any audio device) is it's power supply. The dedicated power supply for one or two channels is a huge factor in the sound quality you get from a free standing rack unit pre amp.
Consider this: A small desktop console uses a tiny little power supply. The X32 uses 1 amp at 120vAC or 120 watts. A classic NEVE console will suck up 1500 to 3000 watts for the same basic signal routing and signal flow layout.
Both consoles do the same thing... one has a lot more power to get the job done.
It's the same deal with rack gear. When you shove 4 channels into 1 rack unit the power supply gets stretched thin. When you consider that a compressor has more active parts than a preamp... the power supply is stretched even thinner.
What does this mean? it means you don't have much head room. It means you can't run those rack mount preamps so hot that they are doing their "warm" thing... you have to back off and baby the line inputs on the desktop console so they don't sound over worked... then, if you have to use the gain on the desktop console to send to the compressor via an insert you are using a gain stage that could enjoy more power to get the sound to your compressor... then when you return from your compressor you'll have to be fairly conservative because, once again, you are sending sound to a under powered integrated circuit (remember, the big consoles that the small ones are copies of use 10x the power for the same basic signal flow) and if you do it all really well you'll have a good clean sound but it will have 2 extra stages of the signature integrated circuit "color".
It's a "color" that most people have gotten so used to hearing that they don't hear it anymore.
Anyways... someones going to come along and tell you I am full o stuff, :-) but this, in a nut shell is why guys still build full size consoles for guys that buy them, and why small time guys buy a couple channels of adequately powered gear from guys that are passionate about making that stuff. It happens because people think it makes a difference they can hear. Someones gonna come along and tell you I'm full of stuff about that too. :-)
Please understand that I am merely saying that if you want to go for it then don't fool around. Get your self something nice. If you don't have the money just now... save up, and rest assured that the cheap, generic, in the box effect tools are really, really, really good and you should feel confident that you can do great things with them with out spending money on low grade hardware OR fancy name brand digital effects.
Good luck. Have fun! I hope you let your curiosity lead you to first hand experiences so you can form your own opinions about what you, personally, enjoy.
all the best,
mike