Yes, all seats are up for grabs. And you’re right, that we don’t elect the PM directly - by default, the leader of the winning party takes the post. (Theoretically it would be possible for Labour to win and for Blair to lose his seat, in which case they’d have to decide on their new leader straight away. Anyone know if anything like this has ever happened?)
Generally, the parties make sure their leader is in a safe seat, so they don’t need to battle hard in their own constituency. Blair’s Sedgefield constituency is in pure red territory in the grim north-east, Michael Howard has a fairly well-to-do south coast seat, and Charles Kennedy is placed in Scotland, where the Lib Dems have some significant support. One to watch, however, is the Tory’s shadow Chancellor, Oliver Letwin, who is in a position where the Lib Dems may well be able to take his seat.
Yes, they all run around trying to be seen in as many places as possible, shaking hands, smiling for photo-calls. And their focus is always on marginal seats, either those they could easily lose, or those they hope to win. On a local level, the candidates for each seat (and their supporters) try to knock on as many doors as possible, meet as many people as possible, lend as many ‘sympathetic ears’ as they can.
Nope, celebrities don’t get tend to get involved in any great way - but as we don’t have the spectacles of American rallies, at which their presence tends to seem more logical.
The only thing voted for in the general election is the MP for your area. However, May 5th does see some local elections taking place, and those for the Scottish parliament. These would have taken place with or without the general election - the date for the latter was chosen partly as a logistical convenience, because it’s easier to run one campaign for all the elections than to have one now, and one a few months later.