There is no cap on sip bonus, they will stack. Also there are threads for these questions, you don't need to make a new one every time you have a question.
It stacks with the trait. Artefacts don't stack with each other (so you can't have more than one level three sip ring), but sip bonuses from different sources (artefact, concoctions, trait, etc) do stack together. However, there's the Quick Questions and Quick Combat Questions threads for this kind of thing.
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Honourable, knight eternal,
Darkly evil, cruel infernal.
Necromanctic to the core,Dance with death forever more.
Results of disembowel testing | Knight limb counter | GMCP AB files