Which type of entity should I use for editable homepage content?
Sure, there are modules that let you setup "blocks" of service badge/icon widgets for like Twitter, FB, YT, etc.

Look at Widgets, Social Media and Service Links modules.

I've used Social Media (which relies on Widgets) to put a block of badges on most pages via Context. And also to create other badge collection tokens that i've used within Footer blocks and embedded into WYSIWYG entries to show a FB link on the homepage for instance, or a mini-block of service links on a newsletter.