The easiest solution is to block guest checkout. If you still want a guest checkout, you would need to program Captcha into the process. This requires some coding skills.

Also, you can change the payment provider to Stripe, for instance. I think they have better way of handling this.

I think you need this ^-?[1-9]\d{0,2}$|^-0$

You can test your regex in here https://www.regexpal.com

I do not get your question. What does it mean "sell completely free"? Are you planning to sell or provide for free?

Set product of price 0 to be free.

There is no such setting to limit number or items in the cart, but should be relatively simple to alter in the code

There is "$this->cust_data" array in core/lib/cart.php class. This needs to be limited your requirement.

Somehow you deleted your config file:
This file is missing.
/home/moralbxy/public_html/ospures/system/config.php

Check Task manuals :
Tasks:
https://abantecart.atlassian.net/wiki/spaces/DOC/pages/18972714/Tasks+API
Sheduling Tasks:
https://abantecart.atlassian.net/wiki/spaces/AD/pages/15007901/Scheduled+Tasks
There is a cron example how to shedule taks.

Gary, You might have got a notification of the spam post and it was later deleted. I have seen that before.
Good luck with your store!
 

Generally, most of CSSs are in this file https://github.com/abantecart/abantecart-src/blob/master/public_html/storefront/view/default/stylesheet/style.css

You can use browser inspector to see where the exact CSS is located.