Large amount of items and collections

Hi Omeka community,
I am new to Omeka and have been test driving Omeka classic V2.7 for a research institute. The institute has a repository of at least 150K items (pdf text documents), all belonging to one of ~10K of collections. Down the road we can expect to archive more. From what I have read so far, I understand that in theory the only technical limit of this amount of items on Omeka is one of storage.
The institute has two interests in Omeka:

  1. Use as an archive management system: store and manage dublin core metadata of all items. Item collecting is ongoing and evolving.
  2. Build curated exhibitions open to the public based on the repository’s items, adding narrative content and images.
    My main question is in regards to #1. When it comes to user interface on the admin side, is there a recommended maximum number of items and collections to have on Omeka?
    Based on my experience so far, I have noticed one issue that might arise:
    Lets say I have +100K items, divided between 10K collections. The collections have a hierarchy using the collection tree plug-in.
    When adding a new item I want to choose which collection it belongs to, a drop-down menu opens to choose from all created collections. If for instance, I have thousands of collections to choose from, this step could be a bit challenging.
    This is just one example that has come up so far. I would be grateful to hear from anyone in the community who has worked with these amounts of items/collections to learn from your experience.

and here are a list of the plugins I have been using so far:
Admin Images
Bulk Metadata editor
Collection Tree
CSV Import
Dublin Core Extended
Exhibit Builder
Locale Switcher
PDF Embed
Simple Vocab

When the Collection dropdown is open, typing letters will jump to those collections will begin with that letter, which might help with finding the right collection.

Do you want the exhibits you build to share a common site? If you would rather create separate sites, you might consider Omeka S (using the property IsPartOf and HasPart to indicate hierarchy between sets).