You can assume the company you will be producing Smartforms for has a company-wide agreements for the font family and size to be used. Set them up in a Style which can be applied to your Smartforms...
A style can be used to define the Smartform's default settings such as Font family and font size as well as tabulator settings. Paragraphs and Character strings can be defined in the Style, which is then linked to the actual Smartform in the attributes of the latter. By default the SAP system uses style SYSTEM which acts as a nice (and simple) example. Have a look: start transaction SMARTFORMS select the "Style" option and fill in SYSTEM.
If you are using Smartforms with the SYSTEM still in place, you should be ashamed for not using SAP functionality as it was meant. When used properly these settings should avoid having the developer define fonts and paragraph settings in the Smartforms themselves.