The amperage rating of a pair (or even 4 8-D's, we always used to run 4 on our KTA-50's) of large batteries would not even burp at running a few lights.
Part of your maintenance program should be to run an "equalize" charge on your batteries to keep the "fuzz" off the electrodes, adding a load to them just helps keep them healthy. You can set up a separate system if you like of course, but I'd opt for the system source.
Marc is quite correct in that 24 volt bulbs are plentiful. Most auto parts places still carry the simple A-19 style 12 volters though making them very easy to keep on hand. You can also get them through Snap-on, Mac tools, Matco, etc, even in a flourescent style which may suite your purpose better.
