The frequency of walks will vary greatly by individual dog and by how much other interaction/stimulation they get in the home.
However, a reasonable starting point is a good walk every other day - perhaps very early or late or even during a rain storm, to minimise the chances of bumping into anyone. If there are walks you can do that tend to be quieter, even if that means driving somewhere, it is worth doing these. This may mean investing in a good pair of wellies and waterproof gear so that you can remain clean and comfy during your walks.
If there are other things that stress your dog a little bit (e.g. traffic) then try to avoid these too as they all take their toll.
Add to that your weekly secure field booking.
As above, if you do have an incident where your dog gets wound up on a walk, then consider giving them a quiet couple of days to decompress.
On the days inbetween, do a couple of training sessions but make them fun based. This is good for you both and the more FUN you can have, the better everything becomes. The key is for you both to enjoy yourseleves together. The link for Absolute Dogs is a good one for ideas but there are also lots on YouTube (Chiraq Patel, Kikopup are a couple of get you started).
Also think about other ways to provide enrichment. A classic one is to scatter kibble around your garden or home, rather than feed from a bowl. The sniff and search activity not only provides entertainment but the very act of sniffing calms your dog.
Other ways are to have fun training tasks you would find useful. For example, the cliche of bringing you your slippers. Things that mean you can ask for them during the day, your dog gets the stimulation of doing them and also the confidence-boost of getting them right and you get to notice the side of your dog that isn't the stressful reactive bit. So often, someone like reactivity ends up being all you can see (through no fault of your own). But, ime, reactive dogs are some of the smartest and most sensitive dogs. There is a lot too them beyond their fears.