Upgrading a simple plugin from OJS 2 to 3

Hi, we would like to carry over a custom plugin we wrote for OJS 2.4.8 into OJS 3.1.1.

After searching in the forums and Googling, it seems custom plugin upgrade process has not been covered completely yet, apologies if this has been asked.

Our plugin only has only article.tpl and the main inc.php. In the main file, there are HookRegistry LoadHandler, IssueAction::subscriptionRequired and TemplateManager::display.

The plugin seems to be working in OJS 3 as is, without any PHP change.
Are there any specific things that we need to be change / be aware of when using this plugin for OJS 3?

Thank you so much.