I'm also developing my first iOS app and will keep an eye on this thread for advice. Question to the OP, are you just starting out with the learning process or are you ready to start deploying apps you have created?
I just published my first app. It isn't very good. I still consider myself in the learning process. What I find the most difficult is the UI/UX creation. How about you? What's the hardest thing about iOS development?
Right now my main concern is legacy code written in Objective-C. I have looked at taking a side project to maintain an app for someone but because it was written in Obj-C, I'm having some reservations. The good thing is that Xcode integration is the same for both Swift and Obj-C, but the syntax of Obj-C is very different.