The only factor that determines whether you should use sanded vs unsanded grout is the size of your grout spaces. 1/8" and below use unsanded.
Read the instructions on the different sealers. When I used polished travertine I sealed before and after, but i think for the stuff with the pits etc you're expected to partially fill them with grout and not seal before. Not positive.
Well, OK, that's the textbook answer about sanded vs unsanded grout in a travertine backsplash application, but there is texture to consider too; I like a smooth grout there not a rough one that the sanded would give...
I am also not a fan of presealing; I say go ahead and apply, then grout with unsanded grout, then seal - if you want as it's not really necessary in such a dense stone. Plus exactly what are you sealing against anyway?
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