Hi,
Like you I never published a game in public. I create games in my spare free time for our 9 year old daughter.
To answer some of your questions.
1. I believe that in its present form, Construct 3 has a very good future. I admit I downloaded the local version a few weeks ago (still in beta) just for those times when I have bad internet. However the online version works perfectly, also in poor internet conditions. The local version let you save on your local disk. For the online version I save to the cloud which has an added benefit, when your hard disk fails, you still have your work. Personally, I prefer Construct 3. Those hate messages disappeared long ago. Especially in the beginning of the beta cycle with the announcement of the paid subscription, there was a lot of hatred. However, those who are really serious about Construct 3, you find now here on the community. I am very glad that the hate message period is over.
2. Together with the online version and the subscription model, Construct 3 future is secure. The subscription model gives Scirra more resources which they use for further developing this excellent tool. You can login from every computer which has internet with your account and develop your game. Also Scirra was and is very innovating, from the very beginning (I started using Construct 2 in June 2015).
3. I do not know much about it. What I do know is that you always have to be smart with graphics. You have to adjust resolution, sizes to make sure you do not hit any performance issues. A few months ago Ashley made a blog post about this. But whatever tool you use, you need to be sparefull with resources.
4. I have no knowledge about that.
5. There are very good tutorials which can help you with that. Also those Construct 2 tutorials are still very usefull. Also Udemy has many very good courses about Construct 2 and 3 which will help you achieving your goals.
Like you, if I would create a game for public use, I do not like adverts in my games. So I will choose for a one time fee instead of adverts. Many people here seems to be fan of those ad supported games, but when I hear around me, most people don't like them. Personally, I like to buy a game and then play uninterupted without ads. But that is a personal choice for the developer.
I wish I had more free time to develop games with Construct. It is really a very nice tool for creating games both indie and professional. I do not regret my choice for Construct 2 and 3.
I wil recommend Construct 3 for sure.
Hope this helps. I am sure other people can give you more valuable information.
Enjoy creating games!