“Do I need institutional accreditation to pastor?”
It very much depends on what you mean when you use the word “pastor”. There are at least three possibilities I can think of. (1) You are contemplating making a livelihood from preaching and teaching in a local church. (2) You desire the work of an elder and are just using “pastor” in a less formal sense as a synonym for “shepherd”, which it is. (3) You are using the word in a completely informal sense, meaning you just want to care for God’s people even if nobody but the sheep and the Lord notices you doing it.