first few weeks - just read, you need to start understanding your area in more detail. My advice, write at the same time, then you'll have something to show for all the reading. I did little 'essays' on each area e.g. 3000-6000 on each area of research, which are invaluable now I'm putting it all together!
You'll probably start planning out the next few years too, e.g. timescales, important deadlines etc.
You can publish before, I'm trying to. its good because a) you get peer review comments on the work before the viva/thesis submission and b) you're more likely to get a job with publications, but they do take time, time away from the core thesis.
I'm finding it very tough to find employment, there is NOTHING out there to even apply for. BUT you'll be finished in 3 years when they will have probably realised they need to pack their departments full of lively young post-docs because they've not recruited for 2 years.
If you want a lecturing/research job afterwards your best bet will be in the uni you do your PhD in, so volunteer for stuff and make yourself invaluable so they'll be forced to hire you! Obviously you need to be good at time management if you take on a lot of extra work.
Good Luck!