You say you have 5 layers of shingles, are you counting 10 layers thick of shingles over the fascia? Meaning if you look at the bottom course there is 9 shingles under the very first course. When you start tearing off the old layers the bottom layers will be coming off in small pieces and you will be having quite a mess. Be prepared to be doing some wood work and when you get the roof striped check for deflection in the roof deck. Stretch a string from top to bottom and side to side. Check the rafters for cracking, theres been a lot of weight on the structure, be sure to correct any problems before you start to re-roof.
Good Luck and have a big dumpster handy!