2)What is the most complex design you foresee cutting?
The complexity of the design is another important considerations. What is meant by this is primarily the overall size and depth of cut per axis. Do you plan to use the machine for cutting, carving, drilling, or all of the above?
3)What kind of tolerances do you need to hold?
Now this is something that I am sure you have already considered but it is still worth discussing. A router is capable of leaving a near perfect finish while surfacing and overall the tolerances are good.