Hi
With regards to number !.
Does the sequential cards with multiple orders imply you are getting fraudulant transactions? If it is then the solution is purely down to the gateway that you are using for your credit card transactions. If the company has a good security matching feature such as worldpay then it stops a lot of fraud.
Number 2
Adding mods is relatively easier than say oscomerce and its derivatives and according to your skills self modding is also easier than most shopping carts.
Number 3
There a number of bulk uploaders available, some are available in cubecart.org (look under archived forums for now)
Number 4
Also look in the archived forums in cubecart.org there are a number of people there who do good work and you will probaly get a few pm's from this post.
I have been using cubecart for about 18 months now and it works for me, after a loss of data on my server after a maintaince routine I performed, I decided to try oscommerce for a change and for experience. My clients hated it and my traffic and sales dropped by 2/3 with emails from clients saying that they would buy elsewhere because of the change.
Guess what, I soon found some saved backups, reapplied my mods and went back to cubecart and my customers love it.
Regards
Degsey