Pointers for research

Ah, my wheelhouse. Finding them is one thing, actually getting them is another... Some are easier to obtain than others. I know that the Leekley Bible used for the prospective televised reboot of Who is out there on the net somewhere, but for something more substantive... This page here and here on A Brief History of Time (Travel) have citation lists that could help quite a bit on the official production side:

The reference book Downtime is a really good addition if you want to talk about the Wilderness Years from a fan perspective, it goes into a lot of detail about the various ways the show was surviving throughout the 1990s. More Than 30 Years in the TARDIS is a good snapshot of how the show was perceived in 1993, what its particular ethos was at the time. The Trial of a Time Lord's documentaries on DVD go into detail about the mid-80s hiatus, although I would take the specifics as more anecdotal than definitive. John Preddle's article Inside the Dark Dimension is a good baseline for that particular project.

I can't speak to Grade himself (his wikia page is fairly brief), but I do know that Baker's attitude towards him has shifted over the years. An interview at a convention done circa 1994 or thereabouts with Jon Pertwee and Michael Jayston actually has him rather understanding of the decision. That's changed rather markedly over the years, something's occurred between that and his interview with Nick Briggs in This is Colin Baker. Which reminds me of Myth Makers, which could also be another really good resource for that period of the show's history. 

That's all I can think of at the moment, I'm sure there are other citable materials floating around somewhere. Hope it helps and best of luck on your EPQ.