Will Zen Cart work for us? (Pre-Sales Comparison Question)

Hi there.

We are deciding between eCommerce platforms for our business. We've whittled it down to five options (Jigoshop, Prestashop, Magento, Zen Cart, and OpenCart) but may I trouble you for help in assessing the implementation costs?

First of all, to brief you on our functional requirements:

1. We sell SEO link rental services to clients and B2B to other SEO companies. We want our clients to be able to select a combination of link rental services of various strengths, adding for example 20x bronze, 10x silver, and 2x gold links to their cart
2. For every link they order, we need two text fields (the target URL and anchor text). This would mean we need 20+10+2=32 pairs of these two text fields in the above case.
3. Customers should then be able to alter the amounts of each type of link in their cart, then sign up to be billed the cart total amount every month.
4. They should later be able to login to:
   4.1) Change the values in said text fields (64 fields in the above example)
   4.2) Add or remove links of each type (automatically altering the cost of their monthly subscription)
   4.3) Cancel their subscription entirely
5. We should be informed via webhook or email when such changes occur, with just the data items that changed.
6. We also want to charge for reports that have a base price + a per-page surcharge, and a total multiplier. ie: So if a SEO report costs $200 + $5/page, then a 10-page report would be $250, but if they also want us to implement the recommendations in the report, then we multiply the $250 total by 2.5 times, making the new total $625.
7. Finally, we want to automatically email new clients with a once-off referral coupon code that adds two free links to the next order for them and the friend they refer. (ie: We want to add freebies instead of discounting price, and track where coupons are used)

Now, my questions are:

A) How much of this can Zen Cart do already? Please address each point above, because we need a detailed response to make our assessment.
B) How much will we need to spend on plugins to get it happening?
C) Which areas will require custom development?
D) Is there an API for future extensibility? (I believe not?)
E) Is there an audit trail to log staff actions? (I believe not?)

Thank you in advance for your detailed response. I am most grateful for your time.

Paul Harvey
Corporate SEO
+61424225495
skype:harvest316
Sydney, Australia