I have the same basic setup as you are considering. I'm using gecko 201s and the same keling motors on the x and y. As far as motor power is concerned, I'd rather have it and not need it than the other way around. My z axis is a 300 oz/in size 34 motor simply because I already had it. It has no trouble moving the spindle up and down. I built my own power supply using maris' directions at the Gecko webpage. Mine is 36v at 10 amps and is probably overkill for current. 48v and 7.5 amps is probably the better power supply. I'm sure there are more knowlwgeable people here to straighten you out on that. 36/10 works for me. I am also using a Cambell Designs breakout board. I like it for the limit and homing switch options it gives. IMO it makes wiring the whole thing up more foolproof.
One thing you should consider when you wire everything up. I installed fast blow fuses on every line(hot) wire in the circuit. Fuses rated just a little above the amperage for that circuit. This is to insure that any problems aren't daisychained down the line into other expensive pieces of equipment.
The mechanical part was easy for me, being a machinist by trade. The electronics look daunting , but if you take it slow and plan things out it really isn't all that difficult. I had a while where i was having a difficult time getting the motors to do what they were supposed to do. Turned out I just had two motor wires reversed. Hey. I did it, it can't be that difficult, right?
Keep asking questions.