I've linked you to a site which describes the responsibilities of an attorney and the types
http://www.lawpack.co.uk/faq_power_of_attorney .asp#4868
You will see that if your mother is willing and able to grant you power of attorney it is pretty straightforward. However if her mental powers are a bit worn out it is more involved.
Answering your questions, if you feel you cannot DIY and do in fact need a solicitor
(1) Yes
(2) No. Any will do.
(3) Phone around and get as many quotes as you can Budget around �200..