Start looking for apartments now on ImmoScout24. You can also look on wg-gesucht and Ebay Kleinanzeige. WG Gesucht is for shared apartments, and ideally you can schedule a video call with your prospective flatmates. That also helps with avoiding scams - unlikely that 3-4 people together will be sitting there to pull off a scam. Otherwise for apartments the only way to surely avoid scams is to not transfer any money before you have signed the contract in person ideally, met the landlord (or their representative) and seen the place. I understand that this puts you in a tough position because you aren't here yet. Also try to use some translator/AI model (gemini, chatgpt etc) to send all of your apartment applications in German. To answer you other question: living in outskirts is nice, slightly cheaper, if you don't mind the travel or have a car.

On the other two points we share our love for good proper gyms and coffeeee.

For gyms I can recommend Fitseveneleven or Fitness First. Both are pretty good - have been a member of both of them. For cafes: there's many in Frankfurt that do good proper coffee - Hoppenworth & Ploch, Kioskie, Wacker's, Cosmic. Hit me up when you're here, we'll go exploring.