Plugins that are supposed to work on Elgg 3.0 should also work on Elgg 3.1-3.3.

As for my plugins (Tidypics, iZAP Videos, Elggchat etc.) I had no time yet to upgrade all of them to Elgg 3. The plugins I released a 3.0 version of should work on Elgg 3.0-3.3 (but I had not even time to test on Elgg 3.1 or newer!). The plugins I did not make a 3.0 release yet are very likely NOT working on Elgg 3 at all without changes.

For Tidypics and iZAP Videos Rohit made pull requests on github which updates and they should work on Elgg 3. You could try it with these version for the time being (download from https://github.com/rohit1290/tidypics/archive/master.zip and https://github.com/rohit1290/izap_videos/archive/master.zip and renaming the plugin folders after unzipping to match the plugins' names). I hope they work without issues but I could not try them myself. I DO have the intention to update all my plugins for Elgg 3 as soon as have the time to do so and I will very likely build up on the work of Rohit then to make the work go faster.

As for the other plugins of mine I'm afraid I can't offer a working solution for Elgg 3 for the time being.

The hype*-plugins are not longer officially supported. Ismayil released updated versions of his plugins for Elgg 3 though before he stopped his development efforts. You can find the new releases only on github though. For hypeWall see https://github.com/hypeJunction/Elgg3-hypeWall/releases.

The comment data is saved in the database always in the same manner regardless of the type of input. It's the input form where you would have to make the change, i.e. change the field from a text/plaintext input field to an longtext input field. The input form view you need to change / override depends on which field you want to change.