Even though you might not be in active training yet for marathon, you may have longer runs, so I'm going to suggest a different method that will work better for that varied workout.

Because really, taking a big calorie burn day, and spreading those calories out through the week for eating back in essence, doesn't really help the day of the big burn. You really need those extra calories after the workout, replace glucose stores for the next workout.

What HRM are you using, and does it have a VO2max stat and maybe self-test?
If not, is your BMI considered in healthy range for your gender and age?
Because your HRM calories may be very under-estimated actually since you've been running.

What you should do is pick a non-exercise level of activity, might be Lightly Active if you have kids or job on your feet.

Then take your reasonable deficit from that.

Now log any exercise above that, with the calories with the same deficit % taken off, and eat that all back.
That way you get calories when you need them, post workout.
So when you start having 2000-3000 calorie burn on a weekend day, you can eat better for breakfast to get glucose stores built up, and have bigger snacks and dinner to replenish what you burned, to have a good recovery. But you'll still get 15% deficit from that extra burn.

Also, HIIT was designed exactly for you, wanting to do cardio only, but want or could use some benefit from lifting type workout.
Which is all out anaerobic push with rests to repeat several times.

So once a week only (should be no more than 20% of cardio time), try the following workout proceeded by a rest day. You need fresh muscles so you can really push hard, if you aren't pushing as hard as muscles can do when fresh, body will have no need to improve the strength of the muscles. Must be done outside, track with softer surface is good. Many Timex watches have interval feature to make this easier, nicer Polar's do to. Garmins very simple to setup.

10 min warm-up walk with some active stretching in there.
2 min jog at aerobic HR zone.
15 sec all out sprint. Don't think about fact of doing it again, push it as hard as possible for the moment.
45 sec walk decent pace. HR should come down, breathing should return to normal, breath deep.
Repeat 8 times. Hopefully it feels like the 8th rep is as fast as the 1st rep, of course it should feel about the same, and hopefully HR is still reaching the same high level. If not, that means muscle is weak, and it will see improvement big time from this.
20 min Jog in Active Recovery HR zone (aka badly called fat-burning zone). Allows recharging ATP stores and clearing out lactate acid from that effort.
1 min sprint at pace below sprint, but still as fast as you can for the whole minute, may take some practice for that pace to sustain for whole min, but should be just as wiped out at the end of it as 15 sec sprint.
1 min walk.
Repeat 5 times. This is wiping out ATP stores and using lactic acid as best as possible, training system for high aerobic level, low anaerobic level. This is not really HIIT, just intervals, improves breathing and oxygen uptake.
10 min cool-down walk with active stretching.

You could also alternate this weekly with hill sprints. Hill should be no longer than 45 seconds full blast up or walk before the top is reached, walk back down, don't run. Jog on the flats, should be at minimum sprint time x 3 for recovery walking before you jog again, get about 10 hills in there, you should feel done. Really reach out the stride to engage the glutes, should feel pain the next day like you did squats, which you did kinda.

Next day should be rest day, or at most a short 30-60 min run in the Active Recovery HR zone, which will feel maybe too slow, but it is what you need. You need to repair muscles, so don't add any new load they need to recovery from, or you'll waste the interval workout.

So that's 2 days taken care of, now you have time for a 60 min aerobic HR zone run, or actually any cardio like bike ride if you want to give joints a rest from the pounding.

Then the long run day, mid-Aerobic HR zone.
Rest day follows and probably proceeds as it gets longer, just walking for muscle recovery.

So you mainly need to be training the aerobic fat-burning system for endurance, but the HIIT and interval routine will increase your lactic acid level, which also expands your aerobic zone.

So that's 4 days of week of running, with 2 big calorie burn days. If you have time, you should throw some upper body strength training in there, day before long run or 60 min aerobic run, or same day as short recovery run. Got all kinds of options for couple upper body routines.

Because even with eating at reasonable deficit, and enough on days of big workouts, you'll still risk muscle mass that is not used, especially on longer runs. So use that upper body muscle.

For your calorie setup to keep it simple, just change your MFP activity level to Lightly Active, unless truly sedentary, and weight loss goal to maintain.
Fitness goal doesn't matter, unless you actually use that on the exercise tab, most don't even know it's there.

Then go to manually setup your net eating goal, since the above just reset it. Take 15% off whatever they put in there already, change macros to whatever you want, and save.

Now log your HRM calories with same 15% removed, and meet the daily eating goal given to you.