I hate to shingle over. Shingles dont last long enough anyway and shingle overs only last 1/2 to 2/3 of years of all new.
What I want to address is shingles are short lifed a bunch from 'cooking ' from the bottom. 95% of houses have poor inadequate ventilation.Dump all those turbine vents, bubble vents,gable end vents, even power vents,,,,they all dont work as well as you think and shouldnt be used any more.
Strictly ridge vent, with soffet vents and open space up every rafter bay. With insulation baffles to keep them open. Even on a calm day you wont believe how much heat is naturally chimneyed out the top. cant get old style to pass that much.
If soffets cant be opened for air intake there is a special vent you can shingle into roof
I have seen roofers do a real hack job on new roofs, careful who you hire. One of those jobs best direct supervised by eyes on roof,,,or d i y to be sure of what you get,
What part of country you live in makes difference on how much ice and water and "30" pound felt to use,,,most pro roofers want to use 15 pound!!! Plus shortcut flashing process.