add new form to blog plugin

i want to make a plugin that similar to blog plugin but has 'Guest star' form . I want my user can input 'gueststar'

My question is:

1. i use $entity->gueststar = get_input('gueststar') to save the data , it is worked but is it right step ?

2. How to get list of entities that has $entity->gueststar='Lionel Messi' ?