Hello Ana
I believe this should be choice based on your own strengths.
If you know you are a strong team leader and have the knowledge to create great advertisements you should concentrate on advertising.
If you have good in-demand products to sell you should concentrate on your ECA business.
The proceeds from either of these activities will help the other.
You can use funds generated from your SFI business for your ECA qualification or you can use funds generated by your Tripleclicks business to fund your SFI advertising.
This is the beauty of SFI. There are so many ways to build a long term profitable business.