Hello there, I'm back bearing questions

Are moorings generally hard to get? I imagine that if your after somewhere in London they are going to be very difficult however other areas are more likely to have space.
Is it a case of putting your name down months in advance before you even buy a boat, I have visions of purchasing a boat and parking it in the garden until somethings available. Also is it worth buying with a mooring but this then limits your options. Or should you speak to the Marina's before you purchase anything to check that space is available?
Ive seen a few barges that I would have to go and 'pick up' but then have no where to moor them.
Sorry if these questions seem silly but its all new...

Any and all information/advice on moorings would be very helpful.
Thanks in advance