Subehai,
Travertine is a lovely stone and quite easy to work with, although the very small
tile size you like mean that you need to be very careful when cutting, either with a grinder or a wet saw. Don't cut a finger or thumb off!
It's a very soft stone so try and avoid having to make thin cuts as it will break whatever kind of cutter you are using. Can you experiment with the setting out so you avoid or minimise difficult cuts?
Make sure you use a cementious WHITE adhesive. Don't use grey or it
will stain the stone and ruin them.
Trowel the adhesive onto the wall but before fixing the tiles spread a thin layer on the back of every
tile with the flat side of your trowel to fill all the voids.
Are these tiles on a mesh sheet, or individual tiles? If on a mesh, then use a rubber grout float to press them flat against the wall and into the adhesive. If you try and do it with your hands you will end up with tiles that are not flat and don't look good.
Also, if they are on a mesh (this applies to any tiles on a mesh, from mosaic to these travertine 10 x 10's) stagger the sheets on every new row i.e. don't lay one sheet directly above another all the way up the wall. Over a large area you tend to see wider and wider grout lines and from a distance you can see where the sheets are. If you stagger them then you won't have this problem.
I personally never seal travertine before grouting, especially as these are unfilled and need the grout to fill all the voids on the front face. I see others have recommended sealing before grouting, not sure what benefit(s) it gives them, maybe they can elaborate??
Chose an appropriate coloured grout as the grout will actually end up being about 20% of the
tile's surface colour when all the voids on the face are filled with it!
Mapei do a comprehensive range.
Tile shop can help you.
Ceramic tiles are more practical and harder wearing than travertine e.g. they won't stain if they get orange juice spilled on them, or fat and grease from cooking, whereas travertine will. Also, you need to re-seal travertine in line with the manufacturer's recommendations.
But ceramic or porcelain NEVER look or feel like stone, because no two stone tiles are the same.
Pick what you like the most, and give it a go!