CCK recommendation? Needed for user profiles

By custom fields do you mean extra fields ?

If yes did you move on this ? We are looking for a way to edit and fill extra fields from within CB blogs editor.

By custom fields do you mean extra fields ?

Yes.

If yes did you move on this ?

No, it's not implemented in the K2 action of CB Auto Actions yet.

We are looking for a way to edit and fill extra fields from within CB blogs editor.

CB Blogs has no such feature. It's designed to be a simple blog usage and does not have custom field support. At this time such a feature is also not planned.

We'll even a simple blog usage should use k2 extra fields...
They are just required for extra classes, prices, and so on.
That should not be too difficult to implement this support if you want a real blog feature ?

Or at least use an auto action to change extra fields values depending on a CB field value ?

We like integration of CB blogs with CB and CB activity but k2 extra fields support is REALLY needed

It's not that easy. All the field types would need to be converted to CB compatible inputs. Entire object handling for it would need to be implemented. In addition to that the extra field groups is category by category based so anytime you change the category it would need to re-evaluate the entire extra field output. There's a list of things that'd need to be implemented, extremely specific to K2, for all of that to work. So in short it's not going to happen. It would get to the point where I am just duplicating K2 article submit, which makes no sense to do. If you need K2 article submit then I recommend using K2 for that.

We only need one extra field with several values to choose to add extra classes to the item with joomlart JA wall template. That's all

Apart of it we like CB blogs interaction with CB activity and it's easiness of use.

Any idea about how to do it ?
I thought about inserting a CB field in CB blog template with multi select but I don't see how to pass the info to the k2 item

You'll need to edit the blog edit template file to add your input then edit the k2 model file to add POST processing of your new input.