As an update, I went ahead with the purchase from vbskinworks. They allow purchasing the branding removal at a later time if desired.
That will at least let me get the project going and work out later whether to purchase branding removal.
That link in the footer is not the problem. The fact other tens of forums use same skin is the issue. I don't have anything against putting a nice link to the one that made the theme or script, but I won't use something other forums use as theme. If you purchased an unique exclusive theme, then it's OK. if it's used by at least 1 more forum, you'll have to modify again so that it won't look "stock".
Anyway .. congratulations for the purchase. It's better than the default skin anyway