The theory of tap replacement is simple - but in practice it is a nightmare because of the generally tight and inaccessible spaces you are faced with. You will find to succeed you need two extra joints in each elbow. So you might actually find it simpler to replace the entire sink / basin unit when you do the job.
It's normal to fix the taps onto the sink along with the waste befoe the sink goes into place on the wall or in the worktop.
Getting fixings that work with both metric and imperial is easy, look at online providers like screwfix if your local DIY isn't stocking.



