The Siege of Mersadie Hive was a custom scenario lovingly crafted by Arthur. As such, unless your GM is planning to borrow the scenario by hacking together what they hear on this episode and the notes on Arthur's blog, there's really no spoilers to worry about.
As always, be aware that the podcast is not really family-friendly, and features some background noise, if that sort of thing bothers you.
Ah, strategising! One of the nice things about Deathwatch is that you really do feel free to be as tactical and military about things as you want, scouting things out and discussing approaches, in a way that other games don't necessarily support. Partly it's because you're expressly playing expert soldiers who would do exactly this sort of thing; partly it's because charging in headlong is reasonably likely to kill you, so good tactics are really important.
I actually cut out about another forty minutes of shopping and briefing that we flashed back to a little way into this mission, some of which I stapled into the first session to try and keep things coherent while drastically cutting down the time.