How to render entries on a singles page in a specific pattern/order?
How are the entries ordered (by date in a channel, manually in a structure or other?)

Are you using the entries anywhere elsewhere at all?

There are a couple of ways you could go, If the Galleries are related to the Updates, you could create a relationship from one to another using an entries field, and then just have the parent render the child in the same loop to different single page entry templates.

Depending on how the URLs need to be, you could use two different entry types in the same channel or structure.  If you need different URL structure you could always use {type} in the 'Entry URL Format' setting and then use custom routes if needed.

Hope this helps :)

I don't think you need to get as complex with arrays or anything.