Hi Dave

MAKE = Materials to be constructed from.
WEIGHT = Mass to move IE gantry etc
FUEL = Voltage running motors at.
WHEELS = Pinion Size
GEARS = Ratios
Just to give you a heads up

WEIGHT = Mass to move IE gantry ==== Frame steal 80mm by 4mm or 100mm by 4mm or 5mm. == Gantry, either steal or ally. Its quite easy to calculate the weights, it will be the gantry weight thats important, not the frame

FUEL = Voltage ==== The gantry weight will tell you what motors and drivers are required ( most of the time nema 23/4 sometimes geared. ). ==== also, your power pack ratings are important,

WHEELS = Pinion Size ( or ballscrews, ) Again, your gantry weight/style will help you decide this, 16mm or 20mm if ballscrews i suggest ( i dont know enouigh about R&P ), same with rails

GEARS = Ratios ===== This is about the speed and accuracy that you want from the motors, its a curve, higher speed, less accuracy.

Most supplyers of metals give the the weight per meter, and you might even fine something suitable for the frame ( with adjustments ) at the scrap yard if your trying to save a few £.

My opinion if your going the cheep route.

There is no cheap route with motors and drivers, you will just need what you need, and its machine specific

Spindle - ebay 2.2kw, water cooled with VDF around £ 250, Aldi ( or other cheep place ) cheap £ 30 dremile type. You get what you pay for. The cheap one will not last long on even modrate use, but it will cut/mill thin stuff ( slowly ) ( just add a cooling fan ), If you got the mounting plate right on the Z, you could even use a cheep router. You might try with the cheap one, to convince yourself you need to pay for the more expencive one, and £ 30 is not a big loss,

Software -- for what you want to do, Mach3/4 would be good ( £ 120 ), there are cheaper alternatives, some free, but unless you have reasonable programming skills, and a good understanding math, you wont beat mach for the support for newbies. In all honestly, with mach, the £ 120 is worth it just for the support,

I hope with what i have put above you have an idea at what parts you can go cheeper on and what parts you can not. If i was you, i would give myself a scrapheap challange, and go looking for something you can use for the frame, your luck might be in. and what you save on that, put into the electronics.