To answer your questions regarding filters, filters only affect data going forward from the time they are applied to a View. You should follow GA best practices and leave the default All Website Data view unfiltered, this way you always have a 'raw', unedited copy of data available from the time the tracking was installed. It gives you something to compare against. Create a test View for testing filters before then applying them to one or more reporting Views that have been created according to your reporting needs.
Real time reporting in GA does not always work when testing with a mobile device due to a lot of devices batching hits to conserve battery power, the hits often get sent through at a later time and processed into the standard reports, but won't show up in the real time reports when testing.
Using the following methods will not confirm if your IP filter is working or not, as filters, remove the data from going into the GA reports after the hits have already been sent to and processed by Google.
With being on a mobile device, it is likely that your IP is dynamic, in which case rather than having to constantly test and change the IP filter, using something like Ghostery may be a better option.
I dont have any experience with Mobile Apps, however I have used GA Debugger chrome extension
and the following method in the past for remote debugging analytics tracking via android for a web site
If you are using an iPhone, then there is also a good article found here