Please someone correct me if I’m wrong but I believe the intent of the Coalition app is twofold. 1) while providing a widely acceptable template (like the Common App), the folders (sort of like a virtual cabinet) that an applicant can establish early allow him/her to drop in prior materials and searches and useful articles – for later consult when it’s time for application. None is open for anyone to see unless the applicant chooses to upload them formally to the schools. 2) The Coalition app partners provide decent fin aid and retention – so there’s a qualitative discriminator inherent with Coalition app partner schools.
For your question #2) – colleges feel either common app or coalition have enough info by which to judge you. Even if one has more questions/prompts – it doesn’t advantage/disadvantage the user to the schools.
Since you likely won’t need to the virtual cabinet, its utility to you is limited. Probably for ease, I’d simply use Common App for all four.
The Coalition App allows you to store ancillary data (e.g., original writing, research papers. videos) in a “locker” that is associated with your application.
Not to be outdone, the Common App is working out an affiliation with an entity called ZeeMee which will provide the same functionality. Whether the colleges are going to bother looking at any of that stuff is anyone’s guess (I would tend to think not; they probably have more than enough to read it the regular app).
The two biggest differences I can see between the Coalition and the Common app are: (1) the word limits – common app is 650; coalition is “suggesting” 500 words; and (2) which schools are accepting the Coalition app (or which schools are NOT accepting it, I should say; there are only 58 schools that are using it this year)