I strongly recommend reading through the book 'Churchwarden's - A Survival Guide' and 'Handbook for Churchwardens and Parochial Church Councillors'.
Whilst you do not bear sole responsibility of the static pars of the building you are responsible for anything that can be moved in the building. Ask to view the 'Terrier' book to find out all that will be your responsibility. This does include the church plate.
Take a good long hard look at the 'team' responsible for the building. You will be working with this team of volunteers in a voluntary [think trustee] kind of way. Are these people you have rapport with that you can build on or have they made their 'roles' into an inpeneratable mess to understand that even the vicar does not dare poke at too hard.
Not all churches have volunteers for everything. CW's are expected to plug gaps either by delegation or holding the fort. Ask if their is any possibility of an interegnum hoving into view during your period of service.
I take responsibility of oversight for the church weekly reciepts - no-one I can delegate this too. I delegated setting up the altar for services to someone else to do. I still bear the responsibility for the provision of bread, wine, candles and care of church plate used.
Seeting up early for church on Sunday doe snot sound too bad unless you have an 8 am communion service. You would often need to be there just after 7am.
As far as the PCC goes. the CW's are ex-officio officers. You would need to contribute your Cw's report at each PCC meeting. You do need to prep a Cw's annual report for the churches APCM. You will need to provide accounatblity to the Archdeacon and complete parish returns and articles of enquiry. No-one mentions that when they are trying to size you up to take on the Canon Law equivilent of a Charity trustee.
In addition I get safeguarding training to do, CW' info days, extra occasional services such as weddings, funerals and baptisms. I cover for additional seasonal services in lent and advent and other times. I am there for the vicar and take their back. I am responsible for the parish when they are on Annual Leave, on a sabbatical or on retreat and away from the parish. I have on occasion lead services when the person booked to do so has been unable to attend on the day.
I am allowed to delegate but bear in mind delegation is only as good as the people you delegate down to. The buck will often stop with you.