Well outside of interpreting the mouse info (thats a problem in itself); if you want the camera to be controlled (without LERPS i am assuming), you are going to have to do a bit of math (imo)
I am not sure how familiar you are with trig and planar math, but ill try to explain the best i can.
Essentially what you want here, is the camera is free to move on a sphere of radius r; around the object you are focused on, and making sure the camera is oriented such that is looking at it; long story short, after the long math for the position of the camera; simple call your cameraNode.lookAt(objectNodePath).
The math here is a bit tricky but lets take the simple case first; say that we lock the camera on the xy plane around the object whos position is (0,0,0). We want the camera to stay on the circle laying on the xy plane whos radius is r; if we want to adjust the location of the camera thus the cameras position becomes
base.camera.setPos(radius * cos(angle), radius * sin(angle), 0)
where the angle is being adjusted by some means (likely a task).
Now if you also want to be able to move around the sphere (not just on a planar circle); It seems logical to approach the problem with spherical coordinates:
With spherical coordinates we have two angles; one being the angle around the sphere (zenith) , and the other being up the sphere (azimuth). with a little bit of math to foodle with the zenith and azimuth values; the following code can be used to convert spherical coordinates to XYZ position:
base.camera.setPos(radius * sin(zenith)*cos(azimuth), radius * sin(zenith)sin(azimuth), r*cos(zenith))
This clearly will take a bit of foodling if you aren’t familiar with trig and spherical/polar coordinates; but its how i approached a similar problem.
EDIT: After posting realized this type of movement can be achieved by creating a dummy node and setting a pos respective to that then rotating; with distance r away from it; after which call the base.camera.lookat(objectNode) function. But hey trig is so much more fun!
If you need some more help; feel free to ask.