Problem:
How to validate image size for multiple image fields using frontend forms

Solution:
To validate the form field in general you can use the Toolset form's hook "cred_form_validate".

You can find the proposed solution in this case with the following reply:
=> https://toolset.com/forums/topic/trying-to-validate-non-repeating-image-fields-on-front-end-user-form/#post-2334355

Relevant Documentation:
=> https://toolset.com/documentation/programmer-reference/adding-custom-code/using-toolset-to-add-custom-code/
=> https://toolset.com/documentation/programmer-reference/cred-api/#cred_form_validate

Problem:
How to configure automatic post expiration using forms

Solution:
Toolset Forms offers post expiration feature using which you can set when should the post be expired (after defined number of days,weeks,months)

Relevant Documentation:
=> https://toolset.com/course-lesson/setting-up-automatic-post-expiration/