1- Can you give the context. It could mean 'when consent is given'.
2- be up for= be ready/prepared for or want to do. Here, it sounds more like the first
3- stag do = party before a man gets married (women have hen dos)
4- a person who works out whether projects will function without destroying the environment (or finances, etc), to see whether the project is viable
5- the important people who control things
6- moving in that direction
7- blast = explode. here, I think it means make a dramatic landing
8- gig = small rowing boat