I would recommend exporting them to jpeg. I'm not sure why they chose tiff. Did it mention setting a max (in pixels or cm or inches) to the photo?
I use Lightroom (very happy with it) on my PC and MAC both. I fix my mistakes (shoot in raw) then export to jpeg. The jpegs are still largish (3-5MBs) that look pretty good (if I say so myself). If you want I can send you a link of the pictures I have taken.

james

"What can be asserted without evidence can also be dismissed without evidence." C Hitchens