I am under the assumption that the elective deferral limit for defined contribution plans (including Simple IRAs and 401ks) is $18,000. IRAs have a separate $5,500 limit. Does the $18,000 limit include IRAs or is the IRA contribution limit in addition to the standard defined contribution plans' limit?
No. 401(k) contribution limits only apply to 401(k)s, not IRAs. The limits are separate. The IRA may or may not be deductible, based on income thresholds.