I did it in 7 days, but one of our group was getting pretty tired which is why we did it in 7 instead of 6. But we carried camping gear and cooking gear, etc. Staying indoors and not cooking cuts your weight a lot. We also had about 3 days of rain, which made for a messy trail.

I think if you commute 14 miles a day (total of 14) for four or five times a week, that should be good training. Your last day or two might be tough, those are longer mileage days but you could likely do it.

Your plan to have shorter mileage days for the first two days is a good plan, as those are slightly uphill. Your third day would be both up and down, more down than up. Last two are close to flat. The uphill is very subtle, you hardly notice it, but you will find your speed is slightly slower on those first two days because of it and that can be discouraging.

Watch the forecast, if it is wet you will enjoy it less.

I am well aware that Marathon Plus tires are a touring favorite, but there is not a lot of stuff on the trail that could cause punctures. A faster pair of tires for the trip might be more enjoyable. Then go back to the Marathon Plus afterwards for commuting duties. In our group (again, we had several days of rain) we had 35mm width tires on one bike, 47mm on another and 50 on the third. All three of us were happy with our tire choices. So, your proposed 35mm tires should work fine.

ADDENDUM: I wrote the above when I thought you were planning five days, but six days would likely work a bit better.