adding more database columns
You don't have to add new database columns nor tables for new features (it is in fact highly unrecommended). Elgg has a unified data model, which allows you to add new metadata or annotations for Elgg content on the fly. Read more about the database here: http://learn.elgg.org/en/2.0/design/database.html
then editing the php
Editing of existing code is also highly unrecommended. All new features should be added using plugins. The best way to get started is by going through the tutorials: http://learn.elgg.org/en/2.0/tutorials/index.html
Also take a look at the source code of the Likes plugin, because essentially you are just duplicating the logic that it already has.
Awesome, thanks. I'll trawl through the documentation and revisit this.
It actually appears that the like plugin is relatively simple. I may simply be able to duplicate it and edit a few lines.
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