There´s quite some stuff to think about regarding mobile stuff, recently I took that challenge myself and it was quite a cruise.
1 - What is the best way to handle fonts when it comes to a mobile app these day? sprite font?
I think sprite fonts are the fastest option, but webfonts work fine too for me. So I´d go with webfonts, as I think they are a bit easier to handle than sprite fonts.
2 - The best way to have an app published in the Play Store is still by exporting it with Intel XDK or do we have other better options?
Use Cordova CLI. I tried all the Phonegap/XDK etc. stuff... just use the CLI. Once you worked into it it´s easy peasy and much less of a hassle.
3 - Today, for those looking to have an app published in the Play Store, what is the best way to add advertisements using C2? if you make mobile apps/games, what do you use?
Cannot answer that, but I had some troubles with IAP and admob, so it´s disabled right now. For ads I might actually go a different route, instead of using some kind of ad-network, I will try to go the direct route and simply offer banner space, that I can add in myself. I can even add them without updating the app, as they are loaded from the server. (This version isn´t online yet though)
4 - As my application handles various information in text, including some that the user can write, what would be the best way to 'save' these texts for the application to load again later?
There´s a bunch of options for this. The mentioned JSON format is probably the best option. Also you might want to look into local storage.
5 - About text again: is the text box working fine? if the user touches the text box the android keyboard open and work as intended?
Yes and no. Textboxes are a bit on the weird side, and actually quite annoying, as different phones and OS handle it different. Even different android versions make a difference.
When user tap on it, the onscreen keyboard opens fine on all devices. But that´s about the only consistent thing. Now the on-screen keyboard shows and...
- Everything is fine, yay
- The keyboard covers a part or all of the input box, pretty annoying
- The app scrolls up by itself in order to compensate for the missing space
- The whole app shrinks to whatever space is left with they keyboard, also very annoying
I still haven´t figured out how to handle this perfectly. If I go ahead and add a fix so the keyboard doesn´t cover the input boxes, on the phones that already compensate by themselves the app will scroll way too high and at best just looks pretty ugly. Same goes for the phones that shrink it, while this usually happens on iPhones, some android phones have this too. Also it does not happen on all iPhones only on some, where I then need to compensate again, or the phone does it by itself, where I cannot compensate for it. Dunno if someone has a catch-all solution for this.