About 15% of the money is currently in the form of cash, and the remainder is in stocks in a taxable investment account (i.e., not a sheltered retirement account).This is to purchase my own home to occupy it.

Borrowed money isn't taxable, either. 

That gives you a donation deduction and income til you die but a portion of the annual payout is taxable.

GM has regained steam and has added a lot of jobs over the past years.As for property taxes, you can find properties with a lower taxable value, you just have to look.

What I am not sure about is whether the depreciation can be used when you own the house/flat as a common person, not an entrepreneur, I think that in such a case you can only write down the rental income by 30% lump sum and the rest of the money is considered as a taxable income.

We were told that when looking for a property we need to make sure the taxable value on the property needs to be low in order for it to be a good deal.

The contributions will be tax-deductible - meaning that your taxable income will be lowered by the amount you contribute. 

first figure out taxable income.

Do you need the interest repayment to help offset taxable income?

What you can do is look to take out a mortgage that will generate enough in the interest-portion of the mortgage (it will change over time) to offset that taxable income.