Updates to existing app

I have an app that's on both iOs (iPhone & iPad)and Android . It needs a few updates, ideally on both, but I'm on a very tight budget so I'm considering just updating the iOs version depending on the cost.
The developer I had no longer works on apps and is focusing on another area of business so I'm looking for someone that can make these amendments for me.
The app is a data recording app with a Firebase backend.

Updates I need are:
-Certain fields currently only allow 20 characters. I'd like this to be increased.
-Navigation at the bottom currently changes depending on which screen you're in. I'd like the navigation to be static to be in line with design of current apps.
-Add a prompt for users to review the app
-Facebook SDK update (I think it's out of date)

Optional updates, dependent on cost are:
-Calendar integration with push notifications for certain events
-Amendment to the layout of the app to bring it in line with current trends.

Please let me know if this is something you can help with as well as your availability.

Kind Regards,
Sonal