Is there a way to set a default volume for different bluetooth connections?
There are two app in the Playstore you can try A2DP Voume and Bluetooth Volume.

A2DP is an app project hosted on code.google.com

Some features of A2DP:


Captures car location automatically when device disconnects. Automatic car locator. (option)
Each device can be independently configured.
Automatically adjusts the media volume on Bluetooth connect and resets on Bluetooth disconnect. Automatically captures location information on disconnect so you can find where you left your car. Read More




Screenshot (Click to enlarge image)

Bluetooth Volume app feature:


This app is perfect for people that always adjusting the volume on their phone immediately after connecting to Bluetooth in the car. This app will do that for you automatically.
Also has an option to launch a Car Home when you connect to Bluetooth.(You need to install Car Home app to use this feature).


So, I think one of the above apps is what you might be looking for.