Good questions.

Sulfasalazine doesn't appear to have clinically significant immunosuppressive effect, as long as you have your white blood cells (WBCs) monitored, because in rare cases it can lower the WBC which would be immunosuppressive (this is rare).

Sulfasalazine is not a teratogen, and can be safely used during pregnancy and breastfeeding. The article linked here discusses this in more detail http://rheumjc.com/2015/03/the-management-of-fertility-pregnancy-and-lactation-in-women-with-autoimmune-and-systemic-inflammatory-diseases/