Q8, I fully understand we all have lives to juggle and we have to fit our running in around it..there are usually ways of doing so it just takes some thinking. Can you run to work for instance, run in your lunch break or home from work, double days? Do you have access to a gym at work? , I'm not aiming the questions at you just throwing out thoughts to be considered when planning.
I have never done very high milage, I prefer quality over quantity any day and to my mind when marathon training it is more beneficial to do a decent block of long intervals than shuffle round some dead miles. So I view training for 100k the same, I trained well for 26.2 miles, ran a good race, bagged a pb, recovered for 1 week then ticked over for the next 3 weeks. I started the 100k with a walk/run regime and watched all the keen lot go off into the distance. I carried this off until we got the hills and swapped for a walk the hills jog the rest when mud allowed. By half way all the keen lot were coming back to me or dropping out.
At the moment I am training for a 100 miles, longer but same principles. For any distance event, most of it is mental strength anyway.
QB..it's not all about quantity but I would be very scared doing any event off the back of a max of two runs a week. I run train 5 days a week, plus Spin and 2 x strength and conditioning. Just because my longest run was 'only' 26 miles doesn't mean it was the single contributor to my completing 100k...you need to look at the whole package, not one factor.
Doing one or two runs a week means you don't experience running on tired legs feel and you also put yourself at a high risk of injury through peaking and throughing. This is also likely to be some of the reason you are not finding the long run comfortable.
I can recomend reading Relentless Forward Progress: A Guide to Running Ultramarathons.
Too late now for any changes to training but it is a worthwhile read.