Just a word of caution.
You started this thread by proposing to fit a TF1 filter. If you propose to install the TF1 on the return leg to the boiler then you MUST ensure that the pressure relief valve (safety valve) is located between the boiler and ANY valve or isolator....your many photos haven't shown it's present location.
If you imagine closing every valve on the system, then lighting the boiler, the pressure relief valve must be able to discharge the boiling water and steam generated in it...so no valve between boiler and PRV.
On the subject of zone valves and wrong circulation direction, if it were wrong and they were Honeywell or Drayton valves you would hear a bang every time the final one shuts; rotary shoe valves are more forgiving (Satchwell, Danfoss), but in all honesty it sounds and looks like the flow direction has been correct all those years. Radiators don't care which way the water flows, and as said previously, just swap the knobs over if it bothers you. Having said that, my experience is that the system runs quieter when the balancing valve is on the radiator exit, so read up on system balancing and do that after your other work is completed - a properly balanced system is a joy compared to the alternative!
Thanks MM. The TF1 can only be fitted shortly after the hot water feed out of the boiler and before the pump, due to space restriction. I know recommendation is for the TF1 to be fitted in the return leg for best performance, but that's not an option here. All my pipework except for a minimum amount as in the photos is buried underground. Even in the house, the pipework only pops up a few inches to the motorised valves then straight back in to the ground to the rads.
The only pressure release valves I am aware of around the boiler area in the garage is the one fitted to the top of the expansion cylinder? and the AAV fitted on length of 15mm pipe above the pump. The pressure release valve connected to the cylinder has its own pipework running in to the right side of the boiler. I'm not aware of any other pressure release valves between the boiler and the rads? As far as I can see the feed runs from boiler to pump, underground to house via three motorised valves for zone 1heating, zone 2 heating and then hot water, out to rads or water tank, then back to boiler. The water tank of course has a TRV and pressure valve fitted, but I don't think that's what you are alluding too?
On your point re balancing, yes, I intend completing that after flushing. Even though its likely that the flow is right, but the plastic valve knobs are the wrong way round on most of the rads, it has meant I have been turning the rads on and off at the return or 'cold' end, rather at the feed or 'hot' end, this is likely causing havoc with the balance of each rad each time I turn a rad on or off.