What i remember about astro photography is that 1) we let the camera warm up and then took a “dark” frame ( lens cap on) followed by some number of frames of short duration (6-10 sec, maybe as long as 30 sec if no clock drive). Then for processing, the images were stacked with binning software that would align all the images and do the dark frame subtraction. Presto, if all went well, no colour noise and nice round stars !
I’ll dig around and see if i can find the weblinks that were helpful. Also, if you search around for an astronomy club, even if not local, you should get plenty of advice.