2009 iMac as monitor for MacBook Pro/file server

Hi, I've just got a 15" retina, and I'm using a 26" wide gamut monitor, good monitor but I think it's on it's way out and it's only 1080p so quite low res for a 26", gorgeous colours on this monitor and perfect for photo editing but it looks a little ugly and as I said I think it's about to die. I'm connecting my laptop and ps3 though hdmi and just switching cables when I want to use each one.

I'm in the market for a high res screen
I was thinking of the Thunderbolt Display, but don't want to pay 700 for one when it has USB 2 and I think a less reflective model (like the new iMacs) is due out soon.

I'm tempted by a 27" Cinema Display too (~£500), or the old 30" with an adaptor

I use my old MacBook Pro as a file server/iTunes server/plex server and also for some imacros scripts that run 24/7. I have a 2tb nas that I'm looking to sell as its so slow, maybe my router is to blame?

I then occurred to me that a 27" iMac might be the best choice for me here, I see someone selling a 2009 model for 600 and it includes a wireless keyboard/mouse. So for 600 I'm getting a 27" Cinema Display, I get a spare keyboard/mouse i can sell on and I can sell my old laptop before it becomes unsupported on mavericks (worth maybe 300?)

Can anyone see any issues with this setup? If I have my keyboard and mouse set to pair with the laptop rather than the iMac, should plugging in the MacBook to the iMac be a painless experience, or would I be better off with one of the older cinema displays (27" or 30"), and maybe get a Thunderbolt Display when they're refreshed. Can I seamlessly switch between using the keyboard/mouse with the iMac and laptop connected via target display mode, I presume the iMac to be far slower than the new laptop so I'd ideally just use it as a screen, as long as the iMac still worked as a server while the laptop was connected

Connecting the ps3 might be an issue, I think the Kanex hd might be the best way?

 

do you have any problems with this setup?

and i have a few quick questions

1) external peripherals- keyboard/mouse, can they be seamlessly switched between imac and laptop or do you have to go through system preferences

2) can I use the imac as a sort of usb hub for connected hard drives? by connecting the imac and laptop via firewire or gig e, enabling target disk mode on the macbook pro and then sharing the drives connected to the iMac

in an ideal world i'd have access to the imac internal drive and connected usb drives and they'd work over firewire 800 when connected to the imac, then when I undock from the iMac and go sit in another room with the laptop the drives would still be acccessible over wireless sharing, that would be epic

3) colour profiles- I calibrate my screens and i'd 100% calibrate the imac too, and it would be great it when I connected the macbook pro the screen was still calibrated, or if it came up on my macbook pro as a display I could calibrate

basically it has to work and be calibrated every time I plug it in