In my opinion, "to be going to" should be reserved for informal and friendly tones. Although the alternatives vary greatly depending on the context, in the example of "the government is going to impose new regulations", this is what I would substitute "to be going to" with: plans to intends to aims to In the context of "plans" as a noun you could use it this way: arranged/formulated/drafted/created/formed/devised/concocted/scheduled/outlined/organised(BrE) plans to The thing is that you can go in many directions depending on the context, but keep in mind to keep it natural and not be too wordy.

Yes, it is fine to use "going to" in written English. "Going to" can be used in almost any neutral text, including the kind of writing you'll be expected to produce in an exam. For example, in the introductory paragraph of an essay, you could say what you are going to discuss. The only context where the 'going to' future isn't appropriate is in formal notices and documents, for example.

This all depends on the context. Many native speakers use it in written language regularly. You just have to ensure it fits into the context. For example, if you are dealing with something that is fixed and beyond your control in the future (Such as the schedule for a flight or meeting) you would use the present simple and not going to. If something is less certain, you would use will instead of going to. For IELTS, it is not just about using fancy synonyms and collocations, it is about getting them to fit in the correct context too.