Honestly, boundaries in that kind of setup depend so much on the specific people involved, you can't just copy a list from somewhere. I've seen too many folks jump into dynamics because they like the aesthetic or the idea of it without really doing the work. The absolute baseline, before you even get to the specific kink stuff, is basic human respect and safety: enthusiastic consent that can be withdrawn anytime, a clear understanding of aftercare needs, and a solid safeword system that works for both parties. Like, 'red' is standard, but some people need a non-verbal signal if they're deep in subspace. That's non-negotiable.
For the DD/lg part specifically, you have to negotiate what 'little' and 'Daddy' mean for you two. Is it mostly a caregiving and nurturing dynamic with some bedroom play? Or is there a 24/7 element with rules and protocols? The boundaries around that are everything. Some littles need strict bedtimes and chore charts, others just want to curl up with a stuffie and watch cartoons sometimes. The 'Daddy' figure needs to understand their responsibility isn't about control for its own sake; it's about providing a structured, safe container. The boundary there is against using the dynamic to mask actual disrespect or laziness.
Financial control, major life decisions, isolation from friends and family—those are bright red lines for me unless you have years of established, healthy dynamic under your belt and have discussed it to death. Even then, tread carefully. The safest boundary is always keeping your own autonomy and ability to walk away intact. It's easy for the lines to blur, especially when the headspace feels so good, so regular check-ins outside of your roles are crucial. We do ours on Sunday nights, just as our normal selves, no titles, to see if anything's chafing.