2. Some Bells and Whistles
If you're not sure about Facebook or other social media outlets, your site can have its own system for this, too. I used something called Community Builder in Joomla when building my wife's site years ago. There are other similar plugins, as well. The point is that you can set up your own internal version of Facebook. You can add forums and messaging, or you could even make ministries into their own pages like I did. People at my church did not fully understand or appreciate what I did, so it was a bit of an overkill, even though it probably still qualifies as one of the best ministries webpage ever created (I am totally not lying).
Forums or sharing
If you want to monitor forums or answer questions, this might be useful. File sharing used to be a bigger deal, but I would go with Google Drive today. Basically, it's nice to provide a space for your users, but it's not mandatory unless you want to compete for their free time.
Embedded videos and photos
Instead of driving people to your Youtube or Facebook pages, those pages can be embedded into the main webpage so that it becomes the destination. However, you must keep feeding the fire with social media tools. The best part about them is that they are free and they give you the bandwidth. The bad news is that they kind of own at least part of the content, so check that out before you post your most beloved professional photos on those sites.
One of my clients does nothing on his site except update his Google calendar. The main page looks updated and the site does its job. Easy and essential to integrate.
You can add little plugins or widgets for just about anything you can imagine, including the receiving of donations. If you see it on another site, Joomla (and likely Drupal or Wordpress) has a solution that will work. If not, there's a code to embed and stick it somewhere on the site.
Browsers on phones and tablets keep getting better as more and more companies pay thousands of dollars to develop apps for those devices. I'd say that unless you have some really cool idea for what your app is going to do for someone (and make some money or new members along the way), wait and see what you need one for, and then pay the developer some money.