The board houses that I have used - basically those offering 100mmx100mm, for a set price - specifically allow panelizing of multiple designs, if the various designs only have drawn lines, to indicate where to cut them apart, yourself. That is to say, there is only one, outside cut edge, for the whole panel. So, when you import/append the different designs, onto a single panel, you need to remember to go back and change all of the interior cut edge lines, to the silkscreen layer, before submitting it to the board house.
Don't try to cheat their deal, by placing routings/etc., for separation cuts. That will just make them stop offering this option.
I have always found the details, regarding panelization, in the ordering instructions. But, you have to look for it.
Seeed and Itead, do it, for sure...
I cut mine apart with a cheap tile saw. I use a diamond blade, that is a solid circle... That is, no teeth gaps... It came from Harbor Freight... The cheap, black, plastic one. It works absolutely great! Cutting panels is a cool breeze!