It would be nice if you could do that simply and be able to keep them as the default for a given file, but FileMaker seems to be a bit "buggy" when it comes to default format settings.
If you select a format with no layout object selected, it is supposed to become the default setting for that layout. It does, but I've found the default often changes after you specify a different format even though it is not supposed to. And this only applies to a given layout so you have to either set the defaults with each new layout all over again or have to start each new layout by using Duplicate Layout to copy an existing layout.
Two things you can play with to reduce the hassle:
Experiment with the format painter. With it you can apply specific formats to layout objects already placed on your layout so you can put together a layout and then update them all with standardized formats.
Try creating a "default formats" layout filled with sample fields, buttons, layout text formatted the way you want for your default settings. Then copy and paste these objects as needed to each new layout. With Fields and Buttons, you can paste the copied object, then double click it to specify a different field or different button options.