1) How often do I need to redo the modeling, for example, do I need one for the winter and one for theIt depends on your equipment. If you don't change anything over the entire year, the model will provide much better pointing and tracking accuracy then without a model.
However, significant changes in temperature can change the amount of flexure in the equipment. Thus a new model might provide higher pointing and tracking accuracy. One of the things I have been experimenting with is modeling the changes in the model not accounted for by just atmospheric refraction changes. This functionality may make it into a future release of APCC. It works by analyzing differences in pointing errors over time and temperature. It can do this because APPM saves the temperature, pressure, and humidity with each sky data point. This particular technique uses machine learning to predict and dynamically adjust pointing/tracking rates based on temperature changes.
One other thing that might affect your model if you are not using a permanent pier is ground shifting/expansion/contraction. This can cause your polar alignment to move around a bit and thus affect pointing and tracking rate accuracy.
Luckily, it is very easy to build a new model with APPM. You should be able to do at least 2-3 data points per minute, so in only 30-45 minutes you can have a fresh new model.
2) If I change the camera, do I also need to redo the modeling?Maybe. It depends on the rigidity of the telescope and the difference in weight between the two cameras. Even so, using a model for a different camera will be better than no model.
Author of APCC (Astro-Physics Command Center): https://www.astro-physics.com/apcc-pro
Author of PEMPro V3: https://www.ccdware.com
Author of Astro-Physics V2 ASCOM Driver: https://www.siriusimaging.com/apdriver