I recommend getting a really good monitor, and choosing one that is as large as you can afford.
that's along the lines of what i was going to suggest. if you're doing graphics work, a high quality monitor is essential for color accuracy. i'm eventually going to spec my own computer when i start my business and haven't gotten around to processor etc. research, but have been looking into monitors.
for hardware, get the highest rated heat sink! it will really help with longevity. if you really want to go nuts, you could even do expensive liquid cooling, but there are some really good copper heat sinks out there that are much cheaper and nearly as effective. do some keyword searching for "heat sink reviews" a couple years ago, i found a really good site that tested and ranked hardware including how well various heat sinks cooled PCs down. it might be a small part of your set up, but it's a wise investment to keep it running well. DON'T do overclocking either. that's a good way to stress your hardware.
as to monitors, these are the three top choices i've found. some people at least prefer to work with 24" monitors and find larger ones too big. they're also more expensive.
Dell ultrasharp monitors eg. 24" U2413 @ ~ $430 & 27" U2711 @ ~ $720. they're very highly reviewed for color accuracy, though you need to find the right calibration tools and DON'T use dell's own ones. there seems to be some issues with tech support for dell monitors too making their 3 year warranties useless if you buy them through 3rd parties
NEC MultiSync PA241W 24" @ ~ $1,000. rated to have even better greyscale accuracy than the dell monitors and offer a 4 year warranty. the impression i got was that NEC is "the best" unless you geta really expensive monitor, not that $1,000 is cheap
i THOUGHT i saved the info, but probably didn't because $2,500 (24" model) is a huge investment, but if you can afford it, wacom's graphics monitors let you draw directly on their screen and are really loved by the people that use them and i think they make 27" too. i WISH i could afford one, but will likely go the dell route myself.
as to audio... i've always wanted to do the cubase thing myself, but have always been a decade behind in hardware and software on used computers. when i get a graphics PC, i plan on getting audio hardware and software for it and to get a dirt cheap refurb, probably running linux, to connect to the internet and keep my workstation virus free.
macs do tend to be the computers of choice for artists, but they've ALWAYS been so freakin' expensive except for those toy minimacs you can't hotrod with audio and video cards etc. there will never be a "useable mac" under $1,000. the price of that system is never going to be affordable for working professionals despite pretty decent specked custom PCs being available for $500 or so.
UPDATE: i just learned of a much more affordable alternative to wacom on screen graphics monitors, the Huion gt-190 is only $700 and is 4 star rated on amazon. it never showed up in my search results, but you can bet i'm going to research those. on screen is the only way to draw as far as i'm concerned and the huions are the only affordable option i know of.
if you're interested in graphics monitors, here's the thread where i learned about the huion
http://www.t-shirtforums.com/graphics-design-help/t378657.html
i also learned about the YINOVA MSP19U alternative there as well as found this really nice link with more pen graphics monitors info & comparisons
http://frenden.com/post/54270393581/cintiq-13hd-err-re-boxing-why-i-sent-mine-back
in reading some reviews, it looks like
yiynova graphic tablet monitors are the best value with even better pressure sensitivity than wacom. $620 for a 19" isn't bad. i don't know if the 22" is worth an extra $380, but that's reasonable too.
