Fire Safety Specialists

Without a door I'd just see it as part of the classroom. I'd just want to be sure that if the curtain was closed then it wouldn't in any way block the detection of a fire in the storeroom.

Its hard to say other than if its above a fire door then it probably needs to be fire resisting. If it does then consider having someone install a fire resisting window and then simply mount this inside the frame of that window.

AFAIK there is no requirement for qualification and certifying a job means nothing, legally. It depends more on the products you are using and the exact methodology for applying them according to the manufacturers instructions.

If you're going by BS 5839-6:2019 for domestic properties then is depends on how the property is used and whether its a new build or existing.

Yes. There used to be an exception for less than 5 employees. But this has been removed.