30 patients total, correct? How many had the outcome? If the model can support that many covariates then you can included them. Are any of them categorical variables that will be dummy coded and entered as more than 1 variable?

You can definitely keep a non-significant variable in the model, if it is of clinical relevance.

You may want to look into an exact/penalized, perhaps Firth corrected model, since you have a very small sample.