How much auxiliary workouts for a runner ?

This is a great question ? Well, running is catabolic. There is no question about this. It has loads of impact and it is a long duration endurance activity. So what we actually want is to have a regular training routine what balances out the catabolic nature of running, by reinforcing proper running technique. These won’t eliminate the breakdown effect of running, but can strongly decrease it ! These are your bodyweight strength and conditioning actions, like core training, balance board play, squats and lunges, your athletic drills like high heels, high knees, sirtakis, fast feet, micro plyometrics, trx and so.
This is a constant practice with no cessation ever ! Can be done even while having a big break from running. This will ensure enough stimulation for tendons and joints to not lose strength !
You should incorporate these into your warming up and cooldown. If you had double days, that can mean 4 sets of drills and strength ! 4 x 15min, no big deal !

Then there are the power and explosive strength and big muscular workouts, high impact plyometrics, bounding and sprinting, all out efforts. This is not for maintenance but for building back. The counter force !
These should be also constant, but very gradual. My personal focus is on Kettlebell swings, but I am incorporating hill bounding, hill sprints and hill strides of 7 to 20 seconds 2 to 3 times a week. I also time to time complete a workout with slower athletes to get the motivation and the volume going, however finish a final rep all out. I mean that it is a kind of time trial, all lactic all out. That can be a 200, a 400, an 800 or a 1000m rep.  Running a 1000m all out is extremely catabolic, but if refuelled properly afterwards, the recovery will supercompansate you to a next level, so next time you run repeats, you will be able to handle acidosis and eliminate muscular byproducts way better.
I also incorporate speed work into my routines time to time, or a period of speed with the 200/400 group. That can be a ladder workout with a ladder recovery. 100 120 140 180 200 180 140 120 100. There is no holding back in any of these. A hard classic is a 1500m or miler workout. 200 + 200 + 400 + 200 @ 1500m race pace /R2:00 . In this as well, there is no holding back, no thinking about the next rep.
To reach a level, when you can trust your body that it can handle back to back all out and high anaerobic efforts, you need the pre-requisites. These were the first sections, so a constant proper posture and the daily routines to maintain it. Also the athletic and non athletic high load strength and conditioning what will make your muscles able to push off harder and to develop force more efficaciously.

So, yes. The more you want to run and longevity is already in your mind, the more you should be thinking about cross training. In this case that means every-thing else outside of running. Once you established a routine, this will take no effort, it will be enjoyable and could be done in no time. No really need for 60minute or 90minute sessions. 10 to 20 min every day is largely enough. In 10min I can warm up, train and cooldown. Done and dusted ! 6 minutes of constant play with an 8kg KB, 1minute priming with the 16kg bell, 2minutes of 16kg KB swings, 1minute of Jefferson curls as cooldown. 10 minutes ! When you have these short and snappy sessions every day, then you look at a 3 year long progresion, that can be like 4000 to 5000 minutes every year. That is 250 hours total training time. What if I told you that this year you can train 83 hours more just by adding a couple of minutes a day ? How smart is that ? This is what counts ! Long term progression ! The Big Picture ! Think big, but start small !