AngularJS and Ionic performance is often questioned. The reason is because it does not necessarily comes out of the box. This post list all you need to focus on in order to get the best performance and user experience out of them.
Push notification is always a pain when it comes to find the perfect free service. If you are hosting your WordPress website there is no need to subscribe any of those services. With your server you have already what it takes to send push notifications to your subscriber. No third party service involved, just your WordPress server and your application.