Droid Engineer Archive

I have heard that a data module in a droid allows extra missions to be taken. Is this true?

If so, what is the difference between the different data modules?

Also, can I use a cheap little mouse droid and leave it in my house or do I need a droid I can take with me? And which would be the best droid to take with me?

Thanks for your help.

BTW, I don't necessarily need a bot capable of facing combat, I just need one that has a chance of surviving in case it accidentally aggro's a creature on the way to a target.