"1 - What is the best way to handle fonts when it comes to a mobile app these day? sprite font?"
Yeah, Spritefont works great. Can't imagine what else you'd use. If you can't get it to work properly, let me know. It took some fiddling experimentation and reading to make it work on my end.
"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?"
Cordova export works great for me, then use free Adobe Phonegap build, private build, enable debugging, name version to some letters in C2, otherwise it won't build.
"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?"
Advertisements, I don't know. Seems a really low revenue source, so I though I'd just charge something reasonable for my game, then if you get a decent number of downloads, at least you make some money.
"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?"
Think people use JSON for that or something. You can do some Googling on Scirra site and straight Google. Never needed myself.
"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?"
Think most people frown upon this sort of question unless you get lucky as this is something you could test on your phone with a quick capx easy.
But anyway, think I answered most of your questions. Maybe I can cash in at some point in the future? (wink)