I have several pairs of Lite / Paid applications in the application store (all of them were created earlier than IAP existed). Iโve made a lot of updates for these apps over the past years, so it seems like Apple is doing a great job with the whole idea if you do it right.
1) You cannot buy a paid application from the free application. The best you can do is send the user to the store for your paid application.
2) That should work. In one of my applications, I have an additional icon on the main toolbar that displays the user on the application store page for a paid application.
3) Yes, you are sending two completely different applications. You set up two apps in iTunes Connect each with its own unique app id.
One project with two goals is an easy and proper way to customize your code. For me, I make two archive builds, configure two applications or application updates in iTunes Connect, and send two applications / updates to iTunes Connect. I always keep both apps in perfect sync. Apple always seems to be looking at them together and always pushing them into the store at about the same time. Only once did two receive approval for more than an hour or two.
The main thing to be careful with is the free version. It can be "Free" or "Lite", but not "Demo". The free version should fully function. DO NOT DESTROY UI elements in the free version that are disabled because they only work in the paid version. He will be rejected. If it does not work in the free version, do not mention it in the free version at all.
Most of my application pairs, the free version, allows me to limit the data compared to the paid version. When a user tries to add data for this point, I exit the warning with a good reminder that the free version is a limit and allows them to upgrade. Other than that, there are no other annoying pop-ups offering a paid version. This is normal if you have a button or something else in the free application so that the user can update, just donโt click on your face or pop-up window of any reminder after using X or time. The free version of the application should fully function independently.
Here I take a couple of free / paid apps compared to IAP:
Against IAP: - There are no promotional codes for IAP - You cannot make IAP free for a certain period of time (sale or something else) - Free applications, as a rule, get lower ratings, because any yahoo can be downloaded. - Optional encoding for IAP
Against a free / paid pair: - Two goals, two application releases, two sets of images, two sets of materials in iTunes Connect - Split downloads and ratings / reviews.
Personally, since Iโve been doing this for several years, the extra effort of sending two applications is trivial.
Edit:
One thing I forgot to mention is that there is still no guarantee that Apple will accept the application this way. But there are many examples of such applications, so it should be good if everything is done correctly.