For contacts, I expect the iOS contacts app will suffice.
For Maps, while Apple Maps is fine, Google Maps has more data and is what I have decided to use, but you can try Apple Maps for a while and see if it suits you. It does have Siri integration which is a big plus for me. However, I ride my bike for daily transit, and that is one thing Apple Maps does not support.
Safari is a good browser, but if you use Chrome on Windows or Linux I'd recommend sticking with Chrome. There is a plugin available, which is what I currently use, but that is up to you.
Google photos is available for iOS, so I'd stick with that, as for calendar: The IOS calendar app can be synced with your Google account so I'd stick with that as well.
And for gmail itself: I used the iOS mail app for a long time, which is basic but works well, but it really depends what features you want. I currently use Inbox for Gmail, which is a somewhat alternative client.
Hope this helped!