Tricky question. 1. If you are using fiducials on the snap-off areas then try and have the tab adjacent to these. 2. In many instances your tab locations will be determined by the case in which you are fitting the PCB. You don't want to be filing down the tab stub where it interferes with the housing. The position of card fingers, tracks, pads, shields etc may also be a factor. 3. PCB thickness, size and layout will also be a factor. 4. In general go as thick and as often as you can, keeping in mind you have to cut them out at a later date.
If you can; get your fabricator to do a bare board, (no plating or drilling for cost reasons), mock-up of the design and run these through the oven or wave several times at different angles to see what happens. Once you are satisfied with the result and have several production runs under your belt you may wish to consider having a punch tool made to do the operation in one step - routing takes time and adds costs. You will have to figure out if you can recoup the cost of the tool. Try starting here: 1.6mm to 1.00 mm thickness PCB use a 3mm wide tab of <5mm length every 50mm. Less than 1mm thickness space them every 40mm. The stiffer you make the panel the better for the production staff.
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