Hey Alan,
Ikebana does not envisage uploading own fonts at the moment; you can install additional fonts manually using e.g. this guide, yet it must be noted regarding the Montserrat font – since it originally comes only in two weights (400 and 700, i.e. normal and bold), installing it separately won’t increase the number of variations since no other styles have simply been programmed and designed for that font. When you specify a font in the Theme Options panel of Ikebana the theme automatically includes all possible styles of the font right away.
Sincerely,
Andrii / Satori Studio