Try looking here.
As for interface, ultimarc is the industry standard.
How powerful a pc you require depends on the games you want it to run. MOST of the older games... not so powerful... and modern games tend to need more caffeine... although there are exceptions. Plenty of forum threads about sluggish DK, for example. You won't find specific specs... some overdrive threads can be searched int he forum if you're curious... try bringing mame on a thumb-drive and test drive the pc and game combo in question before you spend the cash.
If you're going with a pc, any pc monitor will do, in a cocktail even LCD is ok in my opinion, and is the easiest plug-and-play option... and you can always enable MAME's scanline and screen-burn options to crap-up the lcd image to look more authentic. But if you really want true authenticity, you'll go arcade monitor, which will require the appropriate interface depending on the model etc. IMHO an arcade monitor in a mame cab is overkill authenticity... but that's just me. My opinion is that the LCD better captures the pixelated image as the designer meant it to be... the poor quality of monitors at the time was a limitation, not a feature.