I needs some suggestions on what to do with this mead

3 weeks ago I brewed up 2.5 gallons of something similar to the JAOM recipe, I used it as my base. I went with White Labs California Ale Yeast instead of bread yeast. I also did some yeast nutrient additions. Primary fermentation is complete I took several gravity readings and have seen no change. I also tasted it and it was surprisingly good. It has also cleared up quite nicely.

My question is about headspace now that the primary fermentation has completed. My 2.5 gallons of mead is in a 3 gallon carboy, if I transfer it into another carboy to bulk age should I add some additional water to it to reduce the headspace? Or should I just not worry about it and bottle it now, would I get any benefit from bulk aging it?

"...if I transfer it into another carboy to bulk age should I add some additional water to it to reduce the headspace?"

As far as topping it off goes it is important to get the liquid as close to the stopper as possilbe to prevent oxidation. You could use water, but may loose some alcohol concentration. You could mix some honey with water and top off. Or I've even heard of people using sterilized marbles.

"Or should I just not worry about it and bottle it now, would I get any benefit from bulk aging it?"

When you bulk age you get a more consistent taste for the whole batch. From my own experience it is well worth waiting a few extra months and letting it bulk age.