Parameter to reduce cache_form for ajax calls

I have a D7 site with the following items:enter the description of the image here

I have a module that adds a multi-step ajax form to several pages, say 80% of my pages. The form is loaded with different data, but the form structure is the same, that is why I use a module.
As you saw on the screen printing, I have captured enabled to allow visitors to write comments and avoid spam.

Most visitors are anonymous but there are also connected users.

The problem I have is that after the form_cache_expiration (for example, it is set to 8 hours), if a visitor wants to continue using the multisep form, he then gets a "non form data" valid "for the URL www.example.com/system/ajax. This means that the user receives an error message and can not continue. I need the user to be able to continue where he left.

That's why I was playing with the $ conf[‘form_cache_expiration’] setting in settings.php setting it from 6 hours to 24 hours. When it is set to 24 hours, the cache_form table usually becomes too big, for example. 5-700MB and that's too much for my hosting plan.

I've enabled cron so that the cache_form is cleaned frequently for expired forms.

I need anonymous users as well as connected users to be able to continue the form in several steps even after 4-5 days.

What are the settings that I should set in the attached printing screen? for example. do I have to cache pages for anonymous users? would it help reduce the cache_form table? I guess that makes no difference
Do I have to set a minimum cache life?
For the $ conf[‘form_cache_expiration’] = I know that I have to configure it on the basis of trial and error, which means that if I set it on 24 hours and that it does not explode, I can l & # 39; increase to reach the 4-5 days that I need.

thank you so much