The method for calculating property tax amounts for rental properties can vary depending on local tax regulations and practices.

I'm sure you and your agent have done your due diligence on the STR regulations in your market, but I would encourage you to analyze the deal as a long term rental and verify the numbers make sense.

I believe they voted yesterday to form a committee regarding new regulations on STVRs in the county.

I know Airbnb has a way of changing listings and even blocking listings depending on the regulations in the city/county.

They should be able to provide personalized advice and ensure compliance with IRS regulations while optimizing your tax strategy.

Also open to different type of rentals: I'm thinking co-housing/co-living can be a nice way to increase returns, so will be looking in Belgian regulation for this as well.. 

Unfortunately, as you probably have found out, the rules and regulations are not necessarily clear on owner occupancy. 

You must analyze all the data (size of properties, # of properties of each size, location of best producers, regulations, # building permits for that size issued in the last year)3.

Simplifying the processes, laws and regulations into a few basic scenarios when in reality each state has a wildly different set of rules, laws and procedures and each county and often municipality has their unique set of procedures within the state3.

Limited partner's test: (Only three test -Under temporary regulations, individuals who are limited partners and meet the more-than-500-hour test, the five-of-10-years test, or the three-year lookback test are treated as materially participating in any activity of the limited partnership for purposes of applying the passive activity rules)De Minimis RuleIf a qualifying real estate professional aggregates activities into a single rental real estate activity and the taxpayer’s share of gross rental income from all of the taxpayer’s limited partnership interests in rental real estate is less than 10% of the taxpayer’s share of gross rental income from all of the taxpayer’s interests in rental real estate for the tax year, a de minimis exception applies—the taxpayer can determine material participation under any of the tests in Reg. § 1.469-5T(a)  that apply to the rental real estate activities.