1) I can't seem to find clear guidance or case law on this, though. If a company's sole activity is managing the rentals it owns (student rentals during the year and Airbnb or similar during summer, so pretty active management), I would think a case could at least be made that this is the company's trade. Are you saying it fails the "badges of trade" test?
2) The goal wouldn't be to avoid the tax forever, it's to keep more profits in the company for long enough to build up another deposit. The surcharge makes growing a company extremely difficult, as far as I can tell. Doubling the 18 months to 36 months would make a huge difference, at least in this case.