In most cases, the PCB fabricators will panelize your design. However, if you choose to panelize, leave min clearance of 1.6mm between boards for break-routing. For V-score panelization, set the space between boards to be zero.

Standard drill bits used for routing the board edge and milling slots or large holes are 0.2 - 6.3mm in diameter and the accuracy is about +/-0.2mm. V-score accuracy is about 0.5mm.

In general, there is no extra cost for complex board shape when it comes to CNC milling. Charging extra for boards with more than four sides is a thing of the past.

PCB milling machines use a round drill bit for milling slots and PCB outlines. Keep in mind that your inside corners will have a radius to them even though your CAD calls out perfect 90 degree corners.

If for some reason you must remove the inside radius then you should specify a non-plated drill in the corners such as this:

Some vendors offer laser depaneling but there are limitations on board thickness and special cleaning steps to remove any burnt material.