If you want your blocks to insert exploded when you drag them from the tool palette, you have to edit the blocks properties. Right click on one of the pipe fitting blocks in your tool palette and select properties. This will open a new window holding all of the blocks properties. There should be an option for Explode and it will be set to No. Change this to Yes and your block will insert exploded by default. You will have to do this for each of your blocks.
For dimensions, I suggest you read up on dimstyles from the help menu to get started. Type DIMSTYLE at the c-prompt to open the dimension style manager. This is where you create dimension styles.