Stepper motor help.

Hi guys just would like some sound advice on what stepper motors to choose from the Zapp Automation website.
I am finally getting to the end of building my small CNC machine and have decided that I would go for the Nema 17 size motors as the machine will not warrant my other Nema 23 steppers and these I have reserved for my big build.
Now the question I would like answering is I have a 240V 5A power supply and a Bi-Polar 3 axis stepperdriver, now looking at Garys site under the Nema 17 motors there are half a dozen or so but which ones will I need.
The small CNC router will be have a Dremel type tool as a spindle or cutting head and the maximum diameter of cutter will be only 1 mm and it will only ever cut to a depth of 4mm max. The machines travel are X = 20inches Y =4inches and Z = 2inches. I will be using some 8mm threaded rod and my own antibacklash nuts for the leadscrews and I am not looking at speed but more accuracy and again I understand the old chestnut "how well have you built the machine!" but rest assured it is accurate enough, if I can get 10-14 inches per minute that is more than enough. My main aim is to get this little one working, understanding CNC and then get my large machine built, so if anyone can recommend the best ones from Zapp I can get these ordered and move on with my build which I hope will be real soon, many thanks guys.

See the tutorial...

I have tried to read this but to be totally honest I am more confused than anything else. Just wanted an expert's advice as to which one they would use to match with what I have, anybody care to help ?

Plugging your numbers into the spreadsheet and trying all NEMA17 motor types on Gary's site shows that the 1684 motors are do-able, but the others are marginal. This assumes you run them using rated current and 24v supply and the efficiency of the screw is around 15% (allowing for your antibacklash nuts on threaded rod) . You don't say what driver you have, but 24ipm should easily be possible, higher may be.

Hi Irving many thanks for your help. The driver I have was from the Alien CNC kit that I prchased about 4 years ago and have decided to use this for my small machine with the Nema 17 motors and keep the 23's for my bigger build and purchase some good drivers for this, so not to let it go to waste I will use it on the little one as this machine will not be demanding so fingers crossed it should work. Once I have learned to use the machine and using CAD and the correct software it may give me the drive then to finish my bigger machine so I can use both of them efficiently. I was going to use a laptop for working the little machine and the big one but have been advised that power issues are a big problem with the Mach3 software. In saying this how would a laptop fair if it was being used with a constant power supply ie being plugged into the mains everytime you wanted to use it and then switched off when not in use ? The reason being is that I really didn't want to keep a computer in a cold shed and this being affected by the weather might be trouble and not safe to use, so the laptop rout was what I was thinking, bring it in, hook it up, do the cutting then bring it inside ?