In BF 2011 11.7.1j it says that the number indicator can be omitted in certain situations. In 11.7.1k it says that one blank cell may be left between columns, again in certain situations. If all conditions are met, can both techniques be used simultaneously?
It also seems to me that either technique saves the same amount of space. Is one preferred over the other?
Yes, both can be used simultaneously. There is no preference in BF2011, my preference would be to omit the space before the number indicator. Keep in mind that one blank cell may be used only when the column headings are no longer than the longest entry.