FYI - I haven't done this but I think, since Flutter's philosophy
is "write once and use everywhere", you can continue developing your app
on Windows and see it on an Android Emulator until its completely done!
Once its done, rent a mac from Macincloud and then clone your repository to your Mac machine. Then use Xcode to generate your ipa file and then upload it to the Appstore via "Application Loader".
If
you decide to go with their "Managed Server" you have to ask them to
install the latest Android Studio for Flutter. I have used their Managed
Server for React-native project, it almost have everything you ask for.
I haven't tried a Flutter app in Macincloud but If you are interested, I can let you know in couple of days if it works or not?
Disclaimer, I am a React-Native developer whose trying Flutter for the first time.