Planning my 1st trip to Italy by end of May. I was planning on purchasing a TIM SIM card from Venice mainly for data and some local calls. If I purchase a local SIM card will all the iPhone interface will be in Italian? My concern if the GPS navigator will be in Italian instead of English.

No. The SIM card has nothing to do with that. Your phone itself will operate as normal. However you may get texts from TIM telling you how to set up, your balance is running low, etc, in Italian. Or not. But probably.

...and you may be better off using Google maps offline or Here maps (offline) and not burn so much data.

Thank you!

If you get the Tim for Visitors plan, you'll have 4 gb of data, which should be plenty for navigating with Google Maps.

https://www.tim.it/tim-visitors-en

The 100 minutes of calls can be used for calls to many foreign countries, as well as for calls within Italy.

With this plan, you shouldn't have any additional costs, unless you send text messages, so you wouldn't get messages about your credit. Text messages are not included in the plan, but with that much data, I would suggest using instead Google messages, Facebook Messenger, or What's App.

You can install an app called MyTIM, found in the Google or iPhone store, which will show you your credit every time you open the app (credito residuo). You have to set up the account: the userid is your phone number, and the password has to be 8 numbers.

Tim for Visitors plan can be purchased online before my trip. But not sure how to pick up the SIM card, etc... Is this something I can do at Venice VCE airport when I land? Or do you recommend buying this plan from Italy when I arrive instead?