i would want a list of customers so you can have a drive round and get a feel for how well priced the work is. buy an underpriced round and you will be regretting it for quite a while.
also, it would be good, if you have time, to work the round with the guy, to meet your cusomers.
it might be an idea to ask him (with your help?) to distribute a letter to his customers explaining that you are taking over from him, with both his and your phone numbers (and possibly a photo of you??). that way everyone would know the situation, especially the older customers; they don't like change much
this will all take time, but i think it would be worth the effort.
GOOD LUCK, it will be hard for the first few months, but keep at it and you'll do great