2) Each taxpayer has their own tax rates to consider - Federal and state tax rates.When determining state tax rates, they need to potentially calculate the state tax rate of the resident state and the state where the property is located in.

IF I'm going to make extra principal payments to pay off a "low(er)" interest rate mortgage early (compared to today's rates), my gut reaction would be to pay off the highest interest rate mortgage first.

This means the interest rate gets bid down to al low as 1% and the price of the homes is bid up to an amount higher than you can sell it for.  

With historic interest rate increases by the Federal Reserve, many predicted doom and gloom for the industry.

Don't keep your home because of the low interest rate.

Are there still opportunities for rental property investing in this current market with the interest rate and houses prices so high? 

This can trigger unfavorable tax rates when the property is sold, plus there are potential loss limitations, transfer issues, distribution problems, etc.  

Highly unlikely anyone would be able to buy that particular note, and if they could, it wouldn’t necessarily be at a discount.

Does resent comparable sales impact office values in same building at all or we only need to look at CAP rates and determine the value based on CAP rates alone?

However, you may find that they offer loans with shorter terms like 15-20 years and possibly with variable rates instead of a fixed rate.