You're talking about previously doing 180 miles a week to doing 700 miles a week, assuming you are talking about doing that distance every day? That's a big jump in amount of time spent on the bike.
With training that distance won't be too ambitious, but it really depends on your fitness and (like you say) what you're carrying, as well as the pace you want to cycle at. Naturally if you want to do 100 miles in 4-5 hours, you're going to need to be a lot fitter than if you were planning to spend most of the day cycling and taking in the scenery.
You're talking about previously doing 180 miles a week to doing 700 miles a week, assuming you are talking about doing that distance every day? That's a big jump in amount of time spent on the bike.
With training that distance won't be too ambitious, but it really depends on your fitness and (like you say) what you're carrying, as well as the pace you want to cycle at. Naturally if you want to do 100 miles in 4-5 hours, you're going to need to be a lot fitter than if you were planning to spend most of the day cycling and taking in the scenery.