chippy,
first - the scanners
- Epson V700 is ok for 4X5 -8X10, but will give you lots of problems with anything smaller, because of film flatness problems and effective resolution (it has been estimated at 2200dpi)
- Nikon CS9000 with glass carrier is a must for MF and tackles 135mm well, beware, a 48bit RGB scan from a 6x6 frame comes out at roughly 700MB each, this means you will need an external disk of 1 terabyte for every 135 6x6 scans!
second - the screen
- just like lenses are essential for taking pictures, a good monitor is essential for elaborating pictures, best monitors are specialized versions of NEC or La CIE, and can cost more than the computer itself, MAC cinema displays are also good, but come behind these...
third, the printer
- a good inkjet printer will give results as good or better than a lab, but you have the advantage of being able to control the printing process - for small volume work they are indispensable, don't waste your time with Epson R2400, because the cartridges are too small, go directly to 3800 or better
fourth, the calibtrator
- you have to calibrate the whole chain, possibly including the printer profiles, so take this into account, as the complete products don't come for free...
fifth, the computer
- for whatever reason Mac's are preferred in this field, I have worked with both a Mac and a PC, and would second the idea that a Mac is better - I have also read that at present you can use the RAM more effectively on a Mac, but this may change as we go, however I have a negative experience with my iMac as far as the screen goes - I started getting lines of burned pixels after a couple of years of daily use, so I'd recommend a professional screen (NEC or pro line Mac) with a normal big case Mac housing
finally, as you may have understood already, the bigger the format the bigger the files, so get a RAID set of external hard drives with several terabyte space, or your storage will overflow after a few weeks
estimated cost to consider for a serious "starter kit" is in the range of 10-15k USD