Hi Iggy,
[My problem with the fairly newly purchased Canon 70D is that I just have the two old Sigma lenses : 17-70mm with macro through the range and the 70-300mm lens that gave me great images when I was on my Tanzanian safari 5 years ago (walking in Arusha game park, & then snorkeling in Zanzibar & later in Lake Tanganyika) Produced 5 great features for various tropical fish magazines. I haven’t invested in new lenses such as the Canon 24-105mm lens @ £425 (http://www.hdewcameras.co.uk/canon-ef-2 ... AhfQ8P8HAQ) as I am still pondering about going mirrorless. I guess I could just come out with the 17-70 lens. What lens will you be using?]Please don't worry too much about equipment, look at it as a learning exercise getting the most out of what you already have. If the evening works for you and you want to go further you would then have a better idea as to the type of lens or accessorises that you might want to invest in. I went on a course on the South Bank a little while ago and two members of the group only had compact cameras. You don't need lots of equipment to get acceptable results.
On that evening I took my Canon 5D with a standard 24-105L lens. It was more that enough for the job at hand. Looking bat at the metadata, the majority of my images were in the 24 to 60mm range. 24mm being the majority. So your 17-70 will be more than enough. This week I will probably take the same lens, along with a standard 50mm and 70-200mm the latter only to have a play with. What I did find very useful was a set of ND graduated filters, they were a godsend when it came to cutting down the glare from some of the buildings as I wanted to bring out the colours in the water. Mine have a 77mm filter attachment if you want to borrow them on the day.
Regarding the tripod, the one you show the link for looks fairly sturdy and quite cheap. The clam locks are better than twist locks and at £45 you can't go far wrong. If you don't want to buy one I'm happy to bring along a second light-weight tripod (not lugging two heavy tripods especially as the second one is a big old Benbo). Also don't worry about a cable release, it will not be needed, but if you don't have one and want to try one I'll bring a spare along.
As I said before, don't get too hung up over the equipment side. If you're taking the Canon (feel free to bring the other camera if you want) we can always supplement any shortfalls.
Hope this helps.
Tom