Create thumbs/gallery from custom fields

I suggest going with a slider plugin like Layer Slider or this
http://www.wonderplugin.com/wordpress-slider/ . You’re right that a plugin search for this kind of topic has the potential to be endless, so look for customizability and extendability in the plugin.

Similarly for going the DIY route. There’s no need to reinvent the wheel. Find a strong jQuery slider, pop the code in, add a little PHP to get your images and you’ll be good to go. For organizing the actual images, I would use a core WordPress Gallery. It will give you the most control in managing your images in the future, will work with any theme, and never need updating.