marketing/IT is NOT a niche, it's a freaking HUGE industry, and the reason for which this matters is because you will have to silo your site differently than you would do with a niche site.
Also, since you've already settled on marketing/IT I would choose the skyscraper (pillar content) technique since there are probably lots of big topics to cover, and these topics are best served with long form content, supported by short form content...
Regarding the backlinks, I would focus only on really good backlinks initially, and point them only to the homepage (with branded anchors if you have a brand, otherwise a mix of everything) and to the main pillars of the site (you should have at least 4-5 pillars, of at least 3000 words each, but preferably more since marketing is such a broad industry and has so many topics to cover).
And the rest of the pages (the supporting ones) can get internal links from the pillar pages, and the occasional quality backlink every now and then to keep them juiced up or something...