Ok, first up. Thanks in advance

The background.
I have been wearing KSO Treks since March this year for as much time as possible. At work I have to wear boots, so I travel in the VFFs and change. Everywhere else I wear the VFFs. EXCEPT for running. I started running in Nike Lunarglides some time back when I got into running. This year I moved into F-Lite 230s for short runs and Roclite 315s for long runs. I have put off running in VFFs until now because this years target for me was an Ultra. Having survived a 100km run, now is the time for some reassessment. I didn't want to risk an injury prior to that run and really couldn't afford to reduce my milage while preparing for it, hence no running in VFFs. Standard weeks running would for me be 3 runs: Tues - 3 miles, Thurs 3 miles, Sunday 26 miles. The vast majority of my mileage coming from the long weekend run.
So this week I feel like I have recovered, and I started running in my VFFs. So I run my usual 3 miles in them and it takes a while to gget used to them but by 1.5 miles I have forgotten about them. Next run is the same, but it is earlier when I stop being so concious of them. Ran an extra time during the week with my OH as she has taken up running recently, so that was a slow and comfortable 2 miles. Then the weekend comes around and I ran 10 miles in them. No real issues, some odd aches etc that appeared and disappeared during the run. I have had calves that are sore when massaged, but fine when walking or running.
Now the question is how far should I take the long runs? I stopped myself at 10 miles, but felt like a half was easily doable.
There is the issue of this years targets:
- Run an ultra (done)
- Run 100 miles at least every month (So far so good)
- Run 1500 miles for the year (On target)
It's the 100 miles a month that could be an issue. Due to commitments, most of that mileage will have to come from 1 run a week. So how far can I take the long runs in VFFs. Realistically I need to be running 20 miles as a minimum on the weekend runs, which if I was in Inov8s would be no real issue.
So should I run short runs in VFFs and long runs in F-Lites for the time being or just go for it in VFFs? Or is there a third way? Will running in F-Lites impact on the learing my body is doing in terms of footfall etc?