Your doctor or pharmacist can tell you if Immodium is okay to take with Lexapro. I would guess it is okay - but it's better to be safe.
Alcohol very occasionally, and then only one or two drinks. On your prescription bottle of Lexapro there should be warnings about "do not drink alcohol with this medication". Alcohol is a depressant - and nullifies the effects of the Lexapro. Also, Lexapro will amplify the effects of the alcohol - meaning you will get intoxicated more quickly.