I would increase the run say about a ten miler. With a good pair of hiking boots eventually but first get your fitness levels up.
No mention of long distance walking?? Look out for a good local walking group Ramblers Association to name one.
I lead walks from ten to eighteen miles. And when they have been on a ex bootie walk they always go home fully refreshed.
Your skills as a bootie include map reading and compass work and what better a way to learn than with a walking group.
Look out for long distance walks there are plenty about.
http://www.ldwa.org.uk/
Long distance walking group have walks from twenty miles to the annual hundred miler. Do not be put off by the old codgers in the groups, many are ex forces and can still show the way to the young uns who arrive.
My old area has a thirty five miler once a year which is fun, monies raised help the fire brigade benevolent fund and the fire brigade mountaineer section who take kids out into the mountains. The challenge is to walk the trail in a day. Nothing hard about this walk! Good cause and fun at the same time
http://www.frodsham06.co.uk/