Garth said:
the tidal forces of the gravitational field approaching a Black Hole (BH)
event horizon are so severe that you are much more likely to suffer from
Not for a supermassive black hole. Saying that the tidal forces there "may not be fatal" is an understatement; they can be so small as to be undetectable near the horizon. Kip Thorne explicitly chose a mass for the hole in "Interstellar" for which this was true.
Garth said:
the accretion disc surrounding it is likely to be so luminous in the very high energy range of the electromagnetic spectrum (gamma rays and x-rays) that it would still be a very dangerous place to be.
This is true for many holes, including practically all the ones we can (indirectly) observe. But there's no reason it has to be true for all of them, particularly very large supermassive ones such as Thorne used as a model for the events in "Interstellar".
This is actually connected to what I said about tidal forces above. Holes which are large enough to accrete significant mass from nearby space, but small enough to still have significant tidal forces near the horizon, will tear apart objects like stars that come close enough to them. That's how accretion disks are likely to form (at least it's one mechanism that is believed to be common).
A hole of the size Thorne used in "Interstellar", however, is so large that, as I said above, tidal forces near its horizon are negligible. That means an object like a star that falls into the hole just gets swallowed whole; it doesn't start to break up until it is inside the horizon. So there's no accretion disk because there's nothing that breaks up infalling matter before it reaches the horizon.
Garth said:
If you traveled through the event horizon there would be no guarantee that you would go anywhere beyond the 'singularity' at the centre.
For a non-rotating hole (the one in "Interstellar" was rotating at near-maximal angular velocity), this is true--in fact you wouldn't even reach the singularity, because tidal forces would tear you apart first. Even if tidal forces are negligible at the horizon, they increase without bound as the singularity is approached in a non-rotating hole.
For a rotating hole, things are different. First, the singularity in a rotating hole is timelike, not spacelike, so, unlike the singularity at the center of a non-rotating hole, it could be avoided by choosing your trajectory appropriately. However, that is only true in a spacetime that contains absolutely nothing besides the rotating hole. Any matter or radiation falling into the hole will be highly blueshifted as the inner horizon (not the event horizon--that's the outer horizon) is approached. The effect of this is to completely change the spacetime geometry inside the event horizon, so that (at least according to best current belief) the inner horizon never forms, and neither does the singularity.
(The technical term is that the inner horizon and everything inside it, including the singularity, are unstable against small perturbations. Note that, strictly speaking, the "smooth" interior of Schwarzschild spacetime, the spacetime of a non-rotating hole, is also unstable against small perturbations; but unlike the rotating case, those perturbations do not eliminate the singularity--they just make the tidal forces you encounter as it is approached chaotically fluctuate.)
(Also note that all of the above is classical--what the correct theory is when quantum effects are included is a hot topic of research, and nobody really knows the right answer at this point.)
