I started using it a few months ago and have only a limited experience with it. I'm using the Windows10 app, which can not post, by clicking share on an image, outside of the app, and choosing Instagram as the sharing app. In this way it works and honestly, although it is one of the worst user interface, and app, I've seen, I find it still better than using the phone.
Format does not need to be square. Landscape is free form, portrait is max 4 by 5. As usual with compression on apps and forum, pictures with too much fine details are rendered worse and it is better to reduce size before posting. It looks like the max dimension is 1080, which I'm using, but I have not crosschecked the info.
Hashtags are the most important vehicle to viewers. I've noticed that it is better to chose moderately large one, in the 100.000 posts for example, instead of very generic one with posts in millions or more where the flux is too fast for the picture to stay on top long enough.
Followers do fluctuate a lot. I often get 10 more on 1 picture only to be back -7 the next day. Some followers are also only there to sell stuff or spam or get you to follow in return. From more experienced friends, getting to followers in the thousands requires a constant stream, posting every day or even several times a day.
Watch out, there is a max number of hashtags. If you type in more, you get the post but not the caption. Error message are very basic: it only says that something went wrong. The solution is simply to reduce the hashtags and it eventually works.
@brunoschroder
