We strongly suggest you look into joining the https://www.aavso.org/.
Here are some useful links:
Let me answer your questions.
1. You want to use any telescope with a longer focal length. You want the star spread out over a few pixels. You will sometimes want to use the DEFOCUS option in the advanced menu of iTelescope.
2. You can use NABG and AGB; however, NABG are typically non-linear up to a specific ADU count, hence why photometry prefers NAGB. AGB camera can still be used but would keep the ADU count under 25,000 AUD for the target star, ensuring you are linear with your measurements.
3. You typically need to keep the target star at a specific ADU count, e.g. under 25,000. This will be dictated by your exposure time, e.g. you may only need a 35-second exposure for a mag 10 star to reach 15,000 AUD counts. You have to run a set of tests to find the ideal exposure time for the given system.
4. What filters do you use? Typically photometric, these are the U, B, V, R, I. Ultravoilt, B = Blue, V = Green (Visible), R = Red, and I = Infrared. You can also use Luminance, Red, Green and Blue. However, you need to make sure your reference star has been calibrated on these filters. Normally when research is being done on an object, they will have data using a specific filter such as V.
4a. You will typically need to calibrate using a known reference star; depending on what you are targeting, you should be able to find this in databases on these objects. To get started and play around, you can skip this step.
5. You then normally take what is called a "time series", a set of repeating exposure of the same target for a period of minutes to an hour, spending on what you are trying to capture. Some objects change brightness quickly, and some slowly. You are trying to plot the target star's or object's ADU count over time. This will produce a graph. In the case of a binary star, the graph increases or decreases in brightness as the other star passes in front of it.
6. Photometry software:
Here is a tread on the topic: