Answers:
Initially a condition report should be conducted on your consumer unit and fixed wiring. results from this test would tell you if your wiring/installation is up to current standard bs7671 and if it complies with regulations.
also, if your consumer unit is at full capacity (does it have the capacity to add another circuit without causing damage to the existing installation) then yes it would have to be replaced purely on the fact that it cannot accommodate an additional circuit.
i hope this helps.
Internal circuity of light could have been damaged when you removed metal casing.
Depends on how far your moving it and what consists of moving it i.e. extending cables, trunking if surfaced run or do you want it hidden in the wall (chased out).
Short answer no, but as the area your wiring into is a special location, i would get a competent electrician to install it.