Proof of funds would be a bank statement or some other document indicating the liquidity you have.

Germany's resilience to global financial crises and its strong fiscal policies create a favorable environment for real estate investment.Moreover, interest rates in Germany remain at historically low levels, largely due to the European Central Bank's monetary policies.

Quote from @Will Cruz: Does anyone know of a Bank that is willing to do a HELOC on an investment property?

The extra 1050 a month definitely helped with the bank.

Quote from @Stuart Udis: You can also reduce your transactional costs by using a bank construction to permanent loan with an earn out.

At this point, I would recommend having a line of credit to cover these things so you don't have money sitting in the bank doing nothing when it could be put to work.I have 33 units, no debt except for mortgages, and excellent income.

For bookkeeping purposes, I recommend designating a separate bank account exclusive to the house hack activities to keep some sanity.

They switch banks and ask for an extension and add another $2500 deposit as a show of good faith. 

Meaning, the bank wants to see that a property cash flows for typically one to two years of tax returns before they count it as income. 

If you want something that looks nice Article and Castlery have some great looking stuff without breaking the bank too bad ($2-3K range).