A. YES, it is possible to set it up using our API so that when someone joins the 3rd party system an account is created in the WMT Software.
If this is possible depends on the 3rd party software.
It would need to be modified so that when someone joins it, it calls the WMT API requesting that a new account is created.

A.
1) Setup an external billing product for selling the credits.
2) Add a billing option to the product.
3) Edit the Notify URL for the product putting your URL as shown below:
~wmtsystemurl~/admin/smsapi.php?memberid=~affid~&credits=#&apikey=XXXX###
# = Replace # with the amount of credits to add when payment is made
XXXX = Put your API Key from Advanced Features.
yourURL.com = Put your domain name.
4) You can then get the URL or ~~ code to use when when editing billing for placing the button throughout your site.

A.
Below is code you can use to create the effect show above:
The first 3 lines are jQuery and Bootstrap includes. If you already have them included you can remove it. Also, it is only needed for the download icon, so if you use a different icon or an image you don't need it.
In the line below change the 250px to be the height of the thumbnail:
.download .overlay i{line-height:250px}
The code below is for the icon. It can be swapped out with whatever you want (different icon, image, text, etc):
<i class="glyphicon glyphicon-download-alt"></i>
Replace "IMAGE-large.jpg" with the larger image that will be downloaded when clicked.
Replace "IMAGE-smaller.jpg" with the smaller image used for the thumbnail.
