Katt,
If you are using your car for work you will need to make sure your policy covers you for business use. Usually your insurance just covers you for comuting to one work place. As you will travel to many different places you will need business use to be included.
Regarding liability insurance, if you work alone you aren't legally required to take insurance but it is advisable. You can get a quote from our website (see below link) if you want to include cover for damage to glass. Most insurance companies offer liability cover for window cleaners but most won't pay a claim for damaging glass.