Yes, you can work on more than one issue at a time, however, I would focus on the issue at the lowest on the scale to begin with, quite simply, because the lowest vibration tends to hold other issues down as well (like an average vibration)
So, one could be, for example, be vibrating around insecurity on money, but vibrating around pessimism on eyes, so I would focus on the insecurity issue, because I find that once the lowest vibrations are cleared, all other issues naturally improve.