Yes at the end of the training you will receive certification coupon.
On https://elearning.sitecore.net/Public/ContentDetails.aspx?id=BC286B8A482C49BD8CB52CE507B666D0 is described what it contains the training.
The purchase of the Sitecore® Platform Essentials for Developers eLearning includes the option to take the Sitecore® Certified Platform Associate Developer exam. Developers who pass the exam become Sitecore® Certified Professionals. Developers can register to take the exam with an online proctored service from anywhere in the world or at a testing center.
You will not get any help from Sitecore if you have issue during elearning training.
Regarding last question (Sitecore® Experience Commerce™ 9 300 on elearning) I suggest to ask Sitecore from your region.
If you have more questions I suggest you to send mail to one of the bellow:
North and South America: email@example.com
Europe, Middle East, Africa: firstname.lastname@example.org
Greater Asia: email@example.com
Australia, New Zealand: firstname.lastname@example.org