I want to change the settings in my flow temp controller for my Mitisbushi ecodan?

I'm fairly hands on and i want to change the settings in my flow temp controller for my Mitisbushi ecodan PUHZ-HW140VHA2 unit for my 3000 square foot reasonably energy efficient bungalow, it's all underfloor heating. It also has a stove back boiler which helps heats the 300l buffer tank for heating.installer company went bust years ago and im struggling to get anyone that knows what they are talking about. I'm trying to make it run more efficiently so. 

I had the ASHP installed in 2014. 

This july i changed a few settings and i think it has been running more efficiently. (my electricity usage would agree with me however it's hard to properly compare in 5 months.

It recently it has been giving me a P8 error(See error table below.) i just reset the error and then it goes off about a week later. Maybe something to do with temperature of return water or something. See questions 1 and 2 below as they explain what settings i changed. 

1) i switched off freeze protection as it seemed overkill. Do i really need freeze protection function? My system literally has 300+ litres of antifreeze and water ( it says 15% concentration ) I live in Northern Ireland and so it never gets that cold. (seems silly to be heating the system up when no water is being called for. 

2)I have the economy setting for water circulation pump switched to active. Would you recommend keeping this on? I think it makes sense to. The system no longer seems to switch on as much through out the day and night as it did before

Also 

3) What would the recommended pressure be in the system. It reads 1.5 bar at moment but i can easily adjust that? 

4)Do i really need legionella prevention if im regularly using the hot water? Ignore pic below-i can't delete it. 

 5) What speed would you recommend running the Tucson-A water circulating motors that come directly to and away from the heat pump.( Inside the house the pumps are set to speed 2.) circulating choices are 1,2,3, auto, PP1, PP2, CP1, CP2. 

6) what temps would you recommend running the system at. 

It's set to 40d for heating underfloor buffer tank and 48d for DHW.

Any advice greatly received.