What size blade depends on thge thickness of the wood and how intricate the patterns is.
You can find a lot of information on my site. Selecting a Blade and Q & A.
Have good tension on the blade, the blade should not move sideways more then 1/8". I prefere good speed. If not enough speed a person might have a tendency of pushing too hard into the blade, this will make the blade cut with a bevel, besides you will loose control of the blade. Let the blade do the cutting.
FD Mike