I have a lot of components in my schematic that run off +5V and I was thinking of making either the top or bottom ground plane into +5v (leaving the other side with the traditional GND plane). If I’m using all through-hole components, and if the board will be 1.6mm thick, does anyone see any electrical/design issues with this plan?
Not really if there is nothing that is sensitive to interference.
Get in to the habit of using a single ground plane now so as your designs become more complex (i.e. more power rails, faster signals, etc) you will be better able to avoid issues that come with multilayer ground planes.
If you have questions shoot me a PM.