Answers

Call a plumbing professional.  That way the toilets can be evaluated.  You would not want to flush money down the drain on repairs if you are going to have to end up replacing the toilets in the near future.  A plumbing professional would be able to go over all of your options, explaining the pros and cons of each.  That way you can make an educated decision on what you should do.

While there are pros to the Nest, there are other options out there that offer more features and better home comfort control.  The Prestige IAQ from Honeywell is a fantastic option. 

The Prestige is a feature rich, internet capable thermostat.  It has a large, full color touchscreen display.  Homeowners have the option of downloading the Comfort Control App from Honeywell at no charge; so it can be controlled from any phone, computer, or tablet.

The Prestige can also eliminate the need for a seperate humidistat to control the humidifier.  It has wireless outdoor sensors, so the temperature and humidity is monitored indoors and out. 

The Prestige has built-in Delta T Sensors.  These sensors monitor the temperature rise and drop of the HVAC system and will alert the homeowner with an email if there is a need for a service call.  Service reminders can also be programmed in to email the homeowner when it is time for annual maintenance, filter changes, and humidifier pad changes.

The Prestige IAQ is the choice for our company when a homeowner wants to upgrade to an internet capable, smart thermostat.

Generally, you would call an electrician to replace the exhaust fans.  In our area, there are a few service companies that provide electrical services as well as HVAC and plumbing.  That way if issues arise where you need another trade, you only need the one company.  Look for a service company that has all of the services you would need for your home.