Before we dig into custom work, I am wondering if any of this is part of Toolset:
Drop down list with ability to enter new items that become part of the drop down list for future use;
Items should be listed alphabetically and if one starts typing the first 3-4 letters, the item choices should come up.
Thank you!
If you mean a Custom Field, to which you can add new options while editing a post, that is not possible with Toolset.
What you can do is add options in the fields configurations themselves, and then use them when editing or adding posts.
If you require custom programming help for this, I suggest checking our the contractors https://toolset.com/contractors/
Please let us know if we can help further with this.
I also suggest, submitting a feature request for this to the Product Management here https://toolset.com/home/contact-us/suggest-a-new-feature-for-toolset/
Thanks!