It has surprised us delivering nearly $60k in gross revenue annually.

Call the offices of some of the custodians that interest you and see how the phones are answered.

Meet-ups via local groups or via zoom calls or private REI clubs/groups.Asking a seasoned agent in each city/county as well as a Banker/Loan officer will also help put a plan together.

I am a self-entrepreneur and know the importance of office space. 

A good gauge of performance for a full time rental is roughly 10% of valuation (A $1M home should generate $100K+ in gross revenue.) 

I believe you can deduct the other business expenses (home office, supplies, repairs, maintenance etc) - but the bulk of it (depreciation) is likely passed on to later years.So first house 2021 - I'll assume 250k purchase price and you put roughly 20% or 50k down. 

I average about $2000 a month in cashflow on the current rental property, and the new property would bring in around $3500 in gross revenue.

Commercial Real EstateGermany's commercial real estate sector, particularly in the office and retail space markets, also offers solid opportunities.

A couple weeks ago I spoke to a loan officer about getting a mortgage.

This does not align with buying most buildings in cash.Once you progress in your investing efforts you may come across more UHNW individuals, family offices and institutions who would take the lower return for limiting risk (all cash deal).