Some quick answers, and links to find the rest.
You do not need to change your licence - if it is a UK issued JAR-FCL licence you can use it till it expires.
There is no charge for an LPC
SRG1174 is no longer valid.
Have you checked that your non-UK TRE is in the list of approved examiners with PLD?
Scheme of charges:
http://www.caa.co.uk/docs/33/269PLSAmd.pdf
CAA EASA transition website:
EASA Licensing and Training Transition | EASA Transition | Personal Licences and Training
CAA EASA FAQs website:
http://www.caa.co.uk/docs/2330/h-FAQs%20May%202012.pdf