Where to start with a new bathroom?

[jingscrivvens]

The bathroom in our house is pretty old (it still has a round pinned socket up at the ceiling!) and finally the sink has cracked all the way through so time to get a new bathroom! (the bath already leaks and the integrated toilet seat is broken so it really is on it's last legs)
The only problem is I have no idea where to start! Do I get a firm in to do it all? Do I buy what I like and then get a firm in?
We don't have a huge budget and don't want to be taken advantage of since we really don't know how to go forward.

Get a couple of quotes to start with and then you'll be able to start working it out. We had one quote with items included and one without. The one included was not as good as I could do online (for identical items) and it added VAT on top so we went with a plumber to do just the fitting and I bought the stuff myself. I got much better quality for the money because I could shop around.
Think about storing the new stuff, it might not work in a small house with no garage/shed.
I used soakology, ideal standard outlet website, walls and floors or topps tiles (ask plumber if they have trade discount) and got grohe taps (amazon was cheapest for those but plumbers sites are cheaper than the more well known bathroom shops).