Question on which plugin(create,update) and which pipeline to use for MS crm 2011

Hello Guys,

I am think of which plugin to use so that my problem will be solved. Let me give you the sceneraio.

I have a entity which has plugin1 and it updates value to my option set. But sometimes I do not want to update value to optionset and want user to select the option set.

When user select the option set or the option set is automatically set by plugin 1 I want to update auto number filed in my same entity.

For the second scenario I am not able to get the correct plugin.

for my first Plugin it is on Create and Pre opration,what should be second plugin.

Both plugin are on same entity.

Any help!!!

Thanks,

Ankush