Audax riders do that kind of distance plus all the time. Loads of audax tips and chat over on YACF. Start with the FAQ’s.
http://yacf.co.uk/forum/index.php?topic=1201.0
From my own experience you may wish to consider some rather uncool bike modifications, to whit:
A saddle with some padding.
Double wrapped bars.
Raising your bars some.
A map board (or gps).
Getting as much kit onto your bike as possible (and out of your pockets, fill pockets will jelly beans).
A granny ring, or at least a cassette with some range.
Wider tyres, 25c plus, whatever will fit.
Tips: plan where you’ll stop (break the route into chunks, gives you a goal). Eat/finish water just BEFORE you stop (prevents overeating). Keep stops to a minimum. Aim for a sustainible pace, conserve energy.