There are different ideas when it comes to petitioning deities, mostly depending on their culture of origin. Petitioning any spirit is not necessary for working a spell.
My approach is to honor the spirit, build a relationship with them, and then petition. I work with my ancestors. If I only talked to my grandmother when I needed money, she would probably feel used eventually.
This is just a way I perceive it.
The number of spells being cast a day, or the number of times the spell is worked does not matter. A common idea for a work is to do the work 3 times a day. Some people have multiple things going around the house. There is nothing wrong with it at all.
Just make sure you don't spread yourself out with too many projects, spiritual or otherwise.