Don't use the topo/aerial tiffs for the entire state. Instead split them into USGS quad grids and open the grid that you are in. File size should be much more managable that way. Do you have to manually change coordinate systems on an i-pad? I know nothing about them or how accurate they are. I have two mapping grade Trimble units that I use daily. A Juno unit (2-3m accuracy post processing) and a XH6000 unit (submeter accuracy post processing)