I might be able to answer some of the questions you have. Octomap accepts sensor_msgs/PointCloud2 message type as its input. (It might accept other point cloud types too). The Octomap research paper contains most of the things you need to know about its background.
I have tested Octomap in a raspberry-pi 3B, which has 1GB RAM, and a 4 x ARM Cortex processor. It can process an octomap in an acceptable speed, with a 4 cm resolution. But I strongly recommend a computer with higher hardware specifications if you need to build a coloured octomap, or if you need a higher resolution.
For localization, you can use ROS navigation stack, which can be aided by your Octomap.