Thanks for posting up here on the Forum, and for the excellent question. As Digital Principles stewards, those of us at DIAL welcome and value any and all endorsers that feel the Principles for Digital Development can bring a clear value to their work and digital practice.
Of course, that includes smaller sized firms. If the Principles can help connect any dots for your clients (e.g. in suggesting best practices), or if they can help socialize important concepts internally (with staff) or externally (with partners, funders, or competitors), we are all for endorsement.
There certainly isn’t a “size requirement” - and you will note several smaller consultancies are already endorsers. For more info on endorsement, check this out. Or if you have questions, holler at me (@Dustin) or @Allana.