Is it obligatory to fast 30 days along with the fidyah if I act upon the opinion of Ibn Baz regarding the ruling on one who abandons prayer, and is it permissible to adopt the majority's madhhab for the validity of fasting to avoid making up days and paying fidyah, and what is the ruling on one who is unable to pay the fidyah, and should I start by making up the three days from last Ramadan, knowing that there are days to be made up and fasts from the year 1436 AH?

Your fast is valid, and you are not required to make up for it nor offer expiation. However, you are required to make up for the prayers you missed, according to the majority of scholars, and to make up for the three days you mentioned only if you are certain of their obligation; otherwise, this belief of yours might stem from obsessive whisperings (waswasah). The advice is to turn away from these whisperings, ignore them, and pay no attention to them, for indulging in them leads to great evil.