Lens & gear advice for wedding in Siberia

Press Correspondent wrote:

I am going to a wedding in Siberia in 2 weeks. There will be a local pro photographer with his wife as an assistant. Based on his website he mainly uses 70-200/2.8 on 5D, but has other f/2.8 glass:

http://likman.ru/main.php ( click on the kissing couple photo for the wedding gallery)

I am a guest there, but I am also expected to act as a backup photographer independent of the main guy. I have no wedding experience, but have no way to get out of this. I do not want to take too much equipment to Siberia. My questions are:

1. Which out of these lenses I should take with my 5D?

50/1.4
17-40, 24-105, 70-200/4 (non IS)
Zeiss 50/2 Macro ZE (manual focus)

2. Should I buy any extra lighting gear in addition to my 580EX-II: a second flash, reflector, soft box, etc.? (Please keep in mind I am not to get in a way of the main guy.)

3. If I were to invest in one extra lens, what lens should I consider? The budget is under $2,000. (I would prefer to avoid lenses scheduled or rumored to be upgraded soon: 24-70L, 35L, or 85L). Should it be wide like 24L or tele like 100L or 135L? Or something simpler perhaps more than one?

4. I have the Gitzo GT3541LS tripod with the Arca Swiss Z1 ballhead, but taking it there and using it at the wedding may be too hard. I am planning to take a monopod with a small ballhead instead. Is this the right choice?

I have extra batteries and memory cards. No second body. Thanks for your advice.