Hi riesar12,
You ask a number of questions which I will answer, but I want to start off with one important point. Not keeping a backup of important data - and these videos and photos are clearly important to you - is a really bad idea. With so many options available to us, both online and locally, there is no reason that files would remain in only one place, and thus vulnerable to loss. This article describes one solution for backups, Apple's Time Machine application - Use Time Machine to back up or restore your Mac. Please note that you should keep a separate backup from iCloud Photo Library. See the last question in this article - iCloud Photo Library FAQ - Apple Support
Specifically -
iCloud Photo Library stores all of your original photos and videos in iCloud, but we always recommend you keep back up copies of your Library. You can download your photos and videos from iCloud to your computer and store them as a separate library, transfer them to your computer with iTunes, or store them on a separate drive.
Since you already have the video files on your Mac you are able to edit and integrate those into more presentable productions using the iMovie application. This page mentions a number of different ways you can use iMovie to create and share your productions - iMovie for Mac. and this page has a lot of good "how-to" resources for iMovie - Mac Apps - iMovie.
Once you have a finished product in iMovie, you can share it in a number of ways. iMovie Theater works with iCloud to make your video available. See this help article - What is iMovie Theater? - iMovie Help. You can also share the movie directly from iMovie, or using iMovie Theater, to iTunes where it can be played locally or through your Apple TV. See these help pages - Share to iTunes - iMovie Help and Share to iMovie Theater - iMovie Help.
I hope this gives you a good place to start with your photos and video, creating great memories!
Thanks for using Apple Support Communities.
Sincerely.