I used 2 oz of French Heavy cubes in a tertiary carboy when I made it. I kept the fruit in, punching down the cap daily, for a couple month, and then racked the mead into a glass carboy on top of the oak. I did my primary and secondary in plastic buckets.
If you decide to use chips instead of cubes, you should taste frequently. Chips infuse a lot quicker than cubes, and so you could over-oak the mead easier.
Either way, once the oak gets to the point that you like it, or just past, then you want to rack off of it and age a little longer. The oak will mellow with some aging and integrate into the rest of the flavor profile