First of all the step up rings should not cause you any vignetting problems. Step rings are cheap so there's not much to consider really. Just buy them.

Do step down rings cause vignetting?

A step-down ring is when your lens diameter is larger than the filter or filter kit diameter. ... The major disadvantage with a step-down ring is that it is highly likely to cause vignetting since the filter is smaller than the lens.

Can I stack step up rings?

You can stack multiple step-up rings together to achieve a larger thread size.